Perhaps a miniseries from KOTOR. One or two episodes per planet. Might be too generic though.
EDIT: if that's too predictable, then I guess anything to do with the more or less distant past. There is a long lore preceding what happens in the movies, and it hasn't been touched on in film/tv.
Such a show could be great, but would also require talented creators to pull off. The current disney shows don't really strike me as something that would precede such masterpiece.
Inspired by this bit about Anakin and Podracing...
I'd like to see a show that is comprised of low stakes single episode plots. Each episode would feature different characters and take place during those periods of time the movies skip over. They'd largely be about character development, world building, comedy, or just following up on untold stories.
Some Examples:
Luke's life before he met obiwan (blasting wampa rats etc)
C3P0 & R2 working for Leia between episodes 3 & 4
Jar Jar Getting exiled and living on his own
Anakins previous podraces & sebulba
The alluded to past adventures of Anakin as Obiwans Padewan