There's another topic kind of like this a little down the page o_o;;
Anyway, my prediction was a season in the Sevii Islands. But allow me to focus on the question at hand: The Indigo League Revisited.
The way I see it, the idea is plausible. Even though the show is no longer at a pace to where it begins different arcs when new games are released, I still think that another season in the Indigo League would be interesting. There would be a lot of little interesting follow-ups on characters from the first season, but I think that if they were to do it, they definitely shouldn't make it any more than a season. Ash would be able to whip all the gym leaders (possibly more than 8 or some different ones, as we saw with Gary's ten badges and many strange badges in the possession of the Marowak trainer in Bad to the Bone) and the interesting episodes would be the ones where old things are revisited. I would love to see Ash do something a bit different than the league tournament, and finally challenge the Elite Four (Lorelei/Prima, Bruno, Agatha, and Lance, not the four from GS). But there are plenty of ideas, I just don't have them. As I said, it would work, but not if it was horribly drawn-out like Johto and Hoenn.
