I'll forever still hold out hope for a Hello!Project act! *_* Although Berryz Koubou is now out of the equation, considering they'll be on indefinite hiatus in spring 2015 ...
Otherwise, my guest wishlist is kinda pitifully small:
-- Tomokazu Sugita (the only seiyuu I really, really want to meet)
-- Kazuki Nakashima (for screenwriting)
-- Hirohiko Araki (... probably the biggest pipe dream of all, but why not)