I have read all of the atla comics and have some ideas about maybe new topics that could be in "lost stories part 2" but these will come from after the defeat of firelord Ozai but before the time of korra. They could range anywhere from a quick 3 page story to maybe a 100 page story (the size of one part of a normal comic)
Ideas:
1. Maybe tophs most dangerous case she worked in during her time in republic cities police. Think about it, it was so dangerous even the chief had to get out of her office and help
2. A fun story about yue having to watch sokka and suki and she gets jealous (this wold be like a quick couple pages)
3. Aang and Katara's first date / thier wedding (shut up zutara fans kataang is canon)
4. flashbacks of toph raising a kid (i think this would be super funny)
Thanks for reading! these are just some of my thoughts. :)