If you are GMing for the next few years, and every 9-12 months is a new campaign, and just the first one is an oldschool elf/dwarf/human only world great, lets get started, especially if when I pitch my dragonborn psion, your answer is 'next campaign'.
If on the other hand you plan on running the same or similar worlds for the next 5-10 years... NO!! I mean HELL NO!!! DOn't resctict half of my choices for more or less ever...
This I never understand. Why do you pitch
mechanics as your character? Why are you devoted to particular game mechanics?
I run a very tight campaign in terms of mechanical options, and the campaign is in that 5-10 year phase you mention.
If you come to me and say, "I want to play this dragon-guy with scales, fire-breathing, and mind powers.", I'm going to be like, "Ok, we can do that. No problem. Here's how you get started with that concept, and here is a plan for getting all the stuff you want in a reasonable time frame."
But if you come to me and say, "I want to play this character that uses a point based magic, and gets a bonus to strength.", I'm going to be like, "That's not even a character. That's just a collection of numbers. What do you actually want to play?" I feel under some obligation to make available the components for a reasonably broad selection of archetypes and character concepts. I don't really feel under the obligation as a DM to make available any particular mechanic for implementing a character, as long as their is some mechanic. Are you really saying you are loyal to the mechanics, or are you just thinking it would be cool to play someone scaly with draconic heritage?
I mean, I guess in theory I can see someone having this awesome idea for a character only he just absolutely has to come from a whole race of humanoid dragonkin or it just doesn't work, but right at the moment I can't think of what idea that might be.
Mostly I find some characters are just dial fiddlers that like playing around with the system as a game of itself. They are the sort of player that has 2 backup characters already created just because they play character creation as it was a stand alone game. And in my experience, so long as you give them enough dials to turn, they are happy. You don't have to give them specific dials to turn, just a sufficiently bewildering array of them. At least, I haven't run into a character that was like, "Gosh darn it, I'm standing on this mechanic."
Or if you say, "I want to play a gnome bard.", I'm going to be like, "So, you want to play a 3' tall, charming, bearded, trickster forest inhabitant with affinity for burrowing animals and some minor magical powers? That's just fine, but does it have to be called a 'gnome'?"
For me, the real sticking point as a DM that I wrestle with the most is whether to offer a 'monk' type character as a legitimate option. I just cringe at the whole 'I beat things with my fists, because they work better than weapons' archetype. It drives me nuts. But some players are like really into the whole, "I'm a guy in a gi running around punching things." idea. It's sort of available in the rules, but it just isn't quite there. You'll never be as competent at beating things down as a guy that invests in doing the same thing while holding pointy bits of metal, or who says, "I can beat things up, because... magic." And I know it makes some of my players disappointed. And I likewise know that I could just allow a PC and ignore the implications for the world. But it is a bridge too far for me.... so far. I don't feel remotely bad at saying, "No gnomes, no halflings, no drow, no dragonborn, no half-orcs... I've got some homebrew races you can look at." But no 'monks' does make me feel slightly guilty.