I really don't believe there'll be clothing customization for any other Pokémon. The problem here is the same problem with 3D Pokémon walking behind you. It's way easier with sprites, but if they don't do EVERY single curve and movement of the clothing, people will attack the game and say how much it sucks because of that small flaw. I believe they'll prefer to play it safe and not include clothing. Pikachu is different. Is was elected to be the mascot of the franchising, and I'm really happy to see how much it's getting now, since I love it, and I've always been using Raichu to battle.
People were also wondering if other Pokémon would get their voices when the Amie trailer with Pikachu speaking was released. So, no clothes for Pokémon. Hoenn contests were never about clothing, they were always about performing smartly. This supposedly battle mode, though, would be really nice.
I don't like the fact that you can MEvo in the contests, since my best Contest Pokémon is my Girafarig, and I do hope old time champions are recognised as such when they attempt to enter a new Hoenn contest. My Girafarig has that full ribbon that sums everything up to Master Rank together, and I really hope they'll do something with it.
btw, I'm happy the Effort Ribbon will be back. I like it.