I've been thinking about possible plot line, and this is what has struck me: Kiara and Kovu are in line for the throne whenever Simba chooses to stand down. But this leaves Kion, Simba's youngest, without a title... and Simba with the fear that Kion may follow the same path of jealousy that Scar once took. So wise old Rafiki makes a suggestion -- give Kion something to do! Something to make him feel just as important. But never did Simba imagine that the Lion Guard game he created for his son would actually become real, when Kion actually manages to save them all. And that would be the contents of that first full length movie.

Perhaps wishful thinking, but I feel like that's the best way to tie all the canon together? Unless they do decide to ignore TLK2...