Yeah, I almost forgot about the GS Ball, good point.
Anyway, Ash really could pay his bulbasaur a visit (very personal point of view, I like bulbasaur, ok?), perhaps stop ignoring all those beautiful dragons out there and capture one, get his primeape back (simply for team balancing) and Max could catch a freakin' pokemon so he'd stop being absolutely useless.
They could and should make an episode about gary and umbreon, but a decent one. It'd be fine in the chronicles, less ash suits me fine.
Finally, brock could evolve mudkip into Swampert (I know some ppl here would just love that...
That's about it, though, 'cause pikachu'll never evolve... damn.