I'd really, really like to see themed planets. I mean, there's already the Iricia tileset and Aquarius base, and a bunch of white/blue/grey/etc. hats and weaponry that could be moved into an ice/winter themed shop. There's the Choros tileset with Aries, and the staff team could easily bring back the nature shop and plonk it onto the new forest/nature/etc themed planet. Did I mention there's also the lava planet (obviously fire) and the conquest tileset (which screams post-apocalyptic earth to me).

I agree that PK Arena needs to be improved in some way. It's terribly annoying when a PKer storms into a base and distracts from the actual attackers.