More analysis from Toph's Fanboy. I am but a messenger; these are Metal's words and not mine. Enjoy.
If the reports can be believed, from the very beginning the Earthbending teacher was intended to show up in the second season to act as Sokka’s foil. This would seem to be the background upon which the “bromance” which is made blatantly obvious between Sokka and the Avatar’s Earthbending teacher throughout the series, via their complimentary senses of humor and the deeper mutual “warrior’s bond” which developed out of this. Most people will not disagree with the presence of this within the series, and it seems likely that this much was intended from the very beginning.
When it gets messy and unclear for the fan-base is when they decided the gender of the Earthbending teacher ought to be female for the sake of humor (in the irony of the character’s abilities versus what would often be expected of her). This invited in the complexities of boy-girl relationship dynamics for heterosexuals, the exact way in which they were bonding becoming a matter of dispute for the fan-base. As the series progresses, Toph seems to take Sokka’s leadership as a given, and Sokka is shown multiple times to be willing to go out his way to help specifically her when the situation requires it; it is unclear whether this part of their dynamic ever would have appeared had Toph remained Sud, or if they are a result of the Earthbending teacher became a twelve-year old girl. It is for this reason that I am hesitant to label their relationship a “bromance”, as I would readily call a relationship between Sokka and Zuko or Zuko and Aang. Again, the two can be very protective of each other in a way which does not seem likely to been originally intended for the guy-guy relationship between Sokka and Sud, and which gives their relationship romantic undertones which it would otherwise not have and which resists their classification as “just friends”, unlike Toph and Aang’s (well, except in the minds of Taang shippers, who have no real basisto work from).
Bryke has called Zutara “interesting”, indicating that it had some potential and might have made for an interesting storyline had not Kataang been intended from the very beginning and developed from that point. However, because eKataang was planned from the very beginning no romantic undertones developed in-world between the two characters; the Zutara-shipping scenes are only apparently as such, serving to play with the minds of the risible shipping audience but in no way serving to develop even romantic undertones between the characters when fully taken in the context of the events of the series which produced them (something the better members of the Zutara fan-base, like RandomGirl, will readily admit). On the other hand, Bryke clearly intended there to be such undertones in the “Tokka”, “asking” (via the DVD commentary for the episode) whether the scene Toph is annoyed that Sokka didn’t thank her for saving his life in “The Serpent’s Pass” ” was an example of “Toph-Sokka shipping”, and then answering in the affirmative. This particular scene could also be read simply as Toph simply just being testy, like any friend could be, that he didn’t notice that she had just saved his life (which is how I originally tried to read it in order to dismiss Tokka shipping), unlike perhaps the scene where Toph kisses “Sokka” on the cheek for saving her life (which is far less debatable); this would seem to validate the reading of a good deal of their interactions as friends as having romantic undertones (which I ultimately had to do), rather than just the most obvious ones (like the kiss “Sokka” received on his cheek from Toph in the aforementioned episode, and her blushing when unable to admit the esteem to which she held him in her life in “Sokka’s Master” and “The Puppetmaster”). After that point in the commentary, however, they moved on to another subject with a “but . . . you know” and laughed amongst themselves about the subject; this apparently would be a reference to their intentions for the shipping they admitted they were doing, something they obviously didn’t wish for the audience to find out at that point. (The commentary would have been filmed before Suki’s return in “The Boiling Rock”, if that means anything to anybody.)
So, does that fact that romantic undertones exist in Toph and Sokka’s relationship mean that they are meant for each other? No. It just means that Bryke preferred to give their relationship such undertones, not that they necessarily preferred that the relationship become anything in the end. If they are playing with our minds on anything, it would be that those undertones were meant to go somewhere, not that they had some sort of implications for the character’s personalities and relationships (which is entirely different than the way they played with Zutarian’s minds, in which they messed around with the stand-off between ex-canon perceptions of romantic undertones and canon nonromantic intentions). In any case, it is decidedly not a good idea to use the fact that Suki was with Sokka at the end of the series to buttress the idea that she was intended all the way through, or even after she showed back up during “The Serpent’s Pass”. When combined with Sokka’s lack of talk about Suki during Season3 until “The Day of Black Sun”, the "joke epilogue" for the series that was produced in July of 2012 (before that season started, and which contained Maiko, Kataang, and Tokka as the “final” couples) seems to suggest the idea that Bryke had not entirely worked out the end of Suki’s story at this point, and were at the very least playing around with the idea that she might not come back – Azula did seem to be moving in for the kill (or severe incapacitation) when she had pinned during “Appa’s Lost Days”, had she not been swiftly interrupted by another Kyoshi Warrior’s attack. The joke-a-louge was clearly playing off of the ending of Harry Potter Book 7 (which had come out that month), with “Kataang” standing in for “Ginny & Harry” (the titular character, and the girl that won his heart), “Maiko” for “Draco + Priscilla” (the titular character’s waivering personal enemy, and the only girlfriend he is seen with for large portion of the time), and “Tokka” for “Ron + Hermione” (the titular character’s two friends who long had un-admitted romantic undertones to their relationship). As an aside, the reason why I picked up so easily on the “Tokka” undertones when I first watched the series (despite hating it with all my guts at first) was because of the similarities it had to Ron and Hermione’s relationship; I hated fictional friendships with romantic undertones in general, and it has taken awhile for me to get over that hatred.
Does a non-shipper have a solid basis for claiming that Suki and Sokka’s relationship isn’t guaranteed by the finale, story-wise? (I do not wish to enter into a debate about what Nickelodeon will allow in a kid’s show at this point in time.) Yes, on account of the fact that the “Sukka” romantic story-arc had no climatic turning point in which it overcame the hurdles to its existence and established itself story-wise, as “Kataang” did by the threat of Ozai taking Aang’s life away being removed, and as “Maiko” did when Mai transformed from a possible temptation for Zuko to stay with the current Fire Nation establishment to a supporter of his cause (if only for him) in the face of cruel punishment. To say that she must be with him, simply because he had to have “gotten the girl” at the end for his story arc to be completed at the end of the finale, is to pre-assume the existence of what one is trying to prove – which is what the rabid shippers do. Yes, the norm is for a series to have completed its character’s story arcs by the intended ending, but completely aside from the matter of Sukka we already know that this was not the case for the Avatar series, given the fact that the “Zuko’s mother” , the “Aang & Zuko as relatives” subplot, and the “Toph’s parents” subplot were all left unfinished at the end despite clearly having a great significance on the character’s story-arcs (much greater significance, I daresay, then the rather frivolous matter about whether someone happened to “get the girl” at the end or not). The Promise is clearly intended to provide a narrative bridge between the original series and the second one, and as such we have already been assured by Gene Yang that “Zuko’s mother” subplot and the “Aang&Zuko as relatives” subplot will have their purposes revealed (even if that doesn’t necessarily mean Ursa will be located within the confines of his three graphic novels). Given the purpose of the comic, it seems reasonable to expect that the other unfinished story arcs will be completed, the “Toph’s parents” story arc having to be resolved in one way or another for her to progress to taking on the positive role as the creator of the Metalbender cops in Republic City. And with the information that “all the relationships are up in the air”, we can certainly hope to expect that the matter of the unfinished “Sukka” story arc and the purpose of the romantic undertones in the “Tokka” friendship will be settled; if people are dissatisfied with the ultimate conclusion of this, that will be their own fault for ignoring the unfinished nature of the series’ story-arcs relevant to the subject – whether by assuming what they were trying to prove (Sukkaneers) or by privileging what they want to see over what actually may be observed (Tokkaneers, including unfortunately myself from time to time). As for me, given the present confusion I think it best that I (and anyone who will join me) simply hold off on claiming that we know what the canon relationship really is, as that results in too much unnecessary bitterness alongside being an utterly untrue statement when Bryke’s intentions remain unclear and the story-arcs remain incomplete – which is why I took off the “This user supports Tokka” and “This user respects Sukka as a temporary relationship” user-boxes off of my user-page.
Feel free to agree or disagree below, so long as it is constructive.