What hints do you think will be dropped in May's possible return?
May becoming a hot-shot world renowned Top Coordinator, possibly going to visit Unova to promote their Contest circuit?
I don't know, that seems legit.
Would Ash's Bulbasaur evolve for May's Venusaur? How would this affect Advanceshipping?
Vineshipping was sort-of made Canon, so I think they might, since a Bulbasaur-Venasaur pairing looks.. weird.
I think it would, if it ever got to see May's Venasaur again.
And Bulbasaur should evolve, I've always wanted it to evolve.