I actually don't think this is where they're going. I think they're going for a "the DM and group chooses modules to add that everyone abides by" style of modular support, but I can't be 100% certain.
Well, if my friends in 3.X wanted to make "Spider-man" I wouldn't go for it, either. Same for making a character who was from the distant future and had a laser gun and plasma grenades. Or a friend who wanted to play any character from any book series or movie, unless that's what the campaign's focus is.
I'm playing for my enjoyment as well, and I intend to immerse as much as possible. If someone else is going to be consistently and constantly breaking my immersion with their character, I'd probably bow out. I really have no interest in playing with them in that particular campaign. If the purpose of the campaign is humor and everyone is making characters to fit into that concept, I'd bow out as it's not particularly attractive to me, personally.
But, by no stretch of the imagination am I being childish by playing in a game where I'm not having fun. I've got a pretty good new player, who was brought into the game a couple years ago (he's 23 years old) by a group of guy in their 40's playing AD&D. They have a very combat-oriented, dungeon-hopping, published-campaign-using, someone-map-this-as-we-go, use-a-battle-grid style of play. He enjoys it, and that's cool. However, I wouldn't play in that style of game in any sort of ongoing campaign, and neither would any of my other players. It doesn't appeal to us. It's not fun for us.
If someone brought in a character that kept reducing our fun, it's not immature of us to not want that character in the game. It might not mean that character being banned, but it very well could mean me or other players stepping out of the campaign.
This is all going to be decided by the group, of course, because it's a social contract issue. That's a plus for WotC, actually. They get to say, "here's how you can model these things, depending on what you're going for" and leave people to sort it out themselves using the tools they've provided. In your group, you can have a "fighter/sword whacker" and some with "martial dailies and healing surges" at the same table. At mine, I can say "we're using these modules; the same rules apply to everyone." Win/win, really. As always, play what you like