Random note:
Those already exist. They are called the Plane of Shadow and the Plane of Radiance [Dr. 321].
So... when is it some random head-canon and when is it just your own personal homebrew cosmology? Cuz I could rant a lot about the latter. A lot.
For the smaller stuff...
I don't do monoculture races, so this does not apply universally, but I like completely ridiculous combinations such as
- Drow that sound like russian immigrants
- Minotaurs that sound like posh british butlers
- Redneck orcs, etc.
P.S. Is there any word on why Sigil is called the Cage? Someone mentioned the idea of it being a prison for Her Serenity, and that name fits rather well, so how much of actual canon could we have there?