Hey I don't really see a need to discuss one specific stage at a time, we should just talk about all of them at once and throw ideas around at the same time.
Final Destination
Battlefield
Smashville
Town & City
Lylat Cruise
Duck Hunt
Wuhu Island
Skyloft (Kinda hope not)
Halberd (Kinda hope not, ceilings being so low give some characters insane advantages)
Kongo Jungle
Delfino Plaza
Castle Siege
Pokemon Stadium 2 (I hope not)
These are the most of the likely contenders for legal stages, with some being more likely than others. There are a few other stages that are possible if the TOs are super liberal and willing to do crazy stages (Mario Circuit, Pilotwings, Woolly World, walkoff stages) but those are some of the likeliest.
As far as Battlefield goes, I feel like it's good against some characters, and very bad against others. I'm not sure how to describe the character archetype that makes Kirby miserable on this stage, maybe someone can help me out. Basically I think that if they have a good projectile or something and FORCE Kirby to approach, he will hate his life trying to approach them if they decide to camp under a platform. I can talk about more tomorrow maybe!