UA process questions

Can someone explain the general UA process? Specifically, I'm wondering how long it will likely take for the Villainous subclasses to be be playable?

There's really no way to know for sure; they don't provide much transparency into that part of the process. They'll be playable whenever Wizards of the Coast decides to put them in a published book. Sometimes they make it pretty clear which release UA stuff might be headed for, sometimes they don't, and a fair amount of UA stuff never goes anywhere at all.

If you like what you see, you can always build it using the homebrew tools and play it today.

But official printing, as wganarokkr said, is a crapshoot on when or if we’ll get it.

And sometimes, UA can come from multiple books, even if they might have a single theme when put into UA, they can be released at different times.