There are actually a few decent "xyz" combos, believe it or not. That have high/decent search volume and even some which companies are bidding on the keywords.
Last night for shits and giggles after public registration opened, I tried to register defghijklmnopqrstuvw.xyz to create a abc. subdomain for it. It was registered.
I was going to develop it into a 26 page website with just the letters of the alphabet and a word (A: Apple, definition) then slap some AdSense on it.