Even if character customization will not feature in ORAS, I have faith that it'll be back big-time in future games. As stated above, Brendan and especially May are established characters, so it would be "sacrilege" to customize them much beyond their well-known appearance. Okay, you could give them different clothes, and maybe even a hat or something, but you can't do much before the player character wouldn't be May or Brendan any more. GameFreak would have to choose between extremely limited customization, kicking May and Brendan out of "their" game, or having no customization at all, and I suppose the third option is the one with the least fan backlash.
That being said, though, customization is a great way for players to create some sort of identity, looking on the screen and thinking "That's my guy!", which is especially notable in Online settings where you can see the avatars of many people at once. Having the player character a customizable avatar allows for a lot of diversity and closer bonding to the character. Contrast the protagonists of D/P or B/W, which I can't remember the appearance of at all (despite having played both games for a couple hundred hours over the years).
Like the special Vivillon, it could potentially also allow players to collect and show off various pieces of exclusive accessories and clothes, if GameFreak were willing to go down that route. T-shirts commemorating a movie premiere, or funny hats for all attendees of some tournament.
All in all, customization is too great a feature to permanently drop, but it wouldn't be appropriate to apply in these games. However, come Gen. VII, and I bet it will be back with a vengeance.
That being said, though, customization is a great way for players to create some sort of identity, looking on the screen and thinking "That's my guy!", which is especially notable in Online settings where you can see the avatars of many people at once. Having the player character a customizable avatar allows for a lot of diversity and closer bonding to the character. Contrast the protagonists of D/P or B/W, which I can't remember the appearance of at all (despite having played both games for a couple hundred hours over the years).
Like the special Vivillon, it could potentially also allow players to collect and show off various pieces of exclusive accessories and clothes, if GameFreak were willing to go down that route. T-shirts commemorating a movie premiere, or funny hats for all attendees of some tournament.
All in all, customization is too great a feature to permanently drop, but it wouldn't be appropriate to apply in these games. However, come Gen. VII, and I bet it will be back with a vengeance.