They rolled this out in March this year in the US (and December last year in India).

I've successfully renamed an old account with an email address I no longer liked. It works quite well on everything 1st party, but does have the potential of causing issues with OAuth on poorly-coded websites that key on email instead of user ID (ie. most of them). You do get to keep your old email address though, so it still ends up working fine in practice.

Holy crap really? Yay! I know a couple of trans folks that will be ecstatic.