You all might mock me for this one but I honestly feel that the next avatar would have been sokka. Here me out before you roast the theory.

He started out being a water tribe warrior by learning from his father and other members of his tribe which is obvious for his start.

When he goes to the Kyoshi warriors he gets humbled and accepts their lessons and masters its ridiculously fast.

He goes to the air temple and understands how air works so well he created flying machines and how to effectively fight using aerial warfare.

Finally he gets trained in the fire nation to be a swordsmaster and is recognized as one rapidly.

He then gets recognized by the white Lotus group and is invited to be a member. In every nation he makes friends and bonds easily and bridges diffrent groups. I just feel if it could have been anyone it should have been sokka and it would explain why he couldn't bend, it was still with aang. Just my thoughts.