Seriously though, do you disallow core classes or races? I originally had homebrew races back when I was playing B/X, but when I converted to 5e it got too complicated to disallow PHB races and classes. So for my new campaign, it was far easier to just make the PHB available for everyone to pick from, even if in my world there are literally only a handful of elves left, and they're mostly remembered as cruel, psychopathic overlords.
Yep, I do.
I started running a public game and basically allowed anything, but told the players that I was not a fan of things like Dragonborn or Tieflings (at least as they are written now). But I had decided that since I was running a public campaign I'd run a more open campaign even though it didn't entirely mesh with my ongoing home campaigns. So of course I not only had a dragonborn monk, but a warforged character as well, which just doesn't fit into my version of the Forgotten Realms that I've been running since '87.
So the new campaign is starting in a small village (Parnast, actually, but it's quite a bit different than the tiny group of buildings in HotDQ), and I require all players to roll up three characters, since it operates as a home-base type of thing so we can play with whichever players show up each week. In this case, one of the characters are required to be human (they make up 85% of the population in town), one can be human or halfling (10% of the population), and the remainder from moon elf, gold elf, half-elf, or shield dwarf, and can be from out-of-town. I might consider a sylvan (wood) elf as well. I'm also limiting the available classes, many of them rewritten.
Of course, the people choosing to join will know all of this up front. I have a booklet of house rules along with a booklet describing Parnast since the majority of the characters will have grown up there and know all of the local lore.
If I decided to run a different type of campaign, then I'd be happy to revisit other options. And some of the options may be available later. My "dragonborn" are half-dragons that are nearly indistinguishable from their human or elven parents (they are the only races that can be half-dragons in my campaign). I've added a lot of new things, though, like humans have a 30%+ chance of having some other bloodline in their heritage that might give them something like darkvision, or resistance to something like cold or poison.
I'm a big fan of things to be more tightly tied to the campaign world. So warforged make a lot of sense in Eberron, for example. In a great many of the cases the lore and history of the races differs from what's published, especially for a lot of the monsters (although I still lean heavily on the published Realms materials). I prefer the core books to have less lore and more descriptive text instead, and then leave the lore to the world-specific books, or at least something that separates out the different worlds like they've done in a few cases. But, I also play in the Realms, and with what they've published to date I can see how DMs that run campaigns in other worlds are in a tough spot with 5e. From what I see in Volo's Guide to Monsters, I'm not in agreement with a lot of the lore they've published for the Realms there either. I just don't like the direction the lore is taking. But that's OK, it looks like there's a lot of good stuff in there, and even the bits I don't like often have germs of ideas that I will use.