So, with the new Avatar coming ouin the future and the Avatar cycle continuing, going from Water to Earth, stands to be sure the next protag or Avatar would be an Earth bender, right?
But what if they really mix things up this time?
What if the new Earth Avatar is from one the farther reaches of the Earth Kingdom? Maybe they could be a sand bender, like in that episode where Aang and everyone went to find the Library? A sand bender who isn't up-to-date with things like in Republic City?
What if instead of a mere youth, they're a delinquent, getting into trouble every settlement? And just as the authorities caught them, it's the same moment they finally tap into their Avatar powers? (It took Aang a few months since he reawakened to water end properly and Korra grasped fire bending quickly, so it'd be different for the new kid as well) Maybe it's be air, as reverse to the Earth element.
And what if, even after realizing they were the new reincarnation, they don't accept it first and, similar to Aang, they run away at first the first season is them running away from the White Lotus, who need to recruit them at all cost, and just understanding their powers before they could finally accept that they're the new Avatar?
And when they get to Republic City, it's caught up to something similar to early 2000s Hong Kong and Team BryKe could play around with how benders and the spirit world have culminated through new tech? The time period with work based on Korra's timeline onwards.
IDK. Just speculating before they make new announcements.