*Pshyuh!*
What was that? That's the sound of me taking a shot in the dark. Here it goes:
Trainer customization may become a reality. Why may this come to be? Well, there's the shot in the trailer of the protagonist looking into a full-length mirror. There could be only three good reasons for that:
1. To reveal his face indirectly before showing him off.
2. To help show off the 3D.
AND/OR (I'm crossing my fingers)
3. To show that clothing customization will be a possibility. Honestly, why else include a full-length mirror in the game? I hypothesize it's in the area where you change your clothing, whether that's your room or a store.
Some other things that support this argument. The games are clearly taking place (at least partially) in "France," which is a renowned fashion hub. Also, I have a feeling that 3D makes customization a more logical and sensible addition. Lastly, like nearly everyone has said, the male trainer is currently identical to Hilbert. I feel that this was just the default outfit Game Freak decided for the new character to wear for this trailer. The fact that only the two outfits are shown may simply be to keep certain features under wraps.
After all, this wouldn't be the first time for trainer customization! I think it's a possibility, but I doubt it's likelihood. Still, a trainer can dream, can't he?