I'm not kitchen sink. I only allow what I "planned for" in my campaign. Now if you talk to me about it before I start the campaign and I can fit it in then I will most likely do it. If your joining an on going campaign you are very likely going to just have to live with things the way they are until I start a new one. You can still ask, because I can often "make things happen/occur" with some thought, but never, ever, expect to be able to play something or use a rule just because its in the WOTC books.
Its my game, not WOTC's, or yours, if that isn't good enough for the player I probably don't want them at my gaming table anyways. All I will promise is that fun is my number one goal, and that in no way means I have to give players all the "candy" they want.
So if i am running the core 3 books only, and that isn't good enough for a player, they can keep on going to someone elses game. Anyone who is more interested in how powerful they can make their character rather than how fun the game is, well, they are likely not to be someone I'll miss having at my games.