So I decided to be "that guy" and look through who Matt Booty follows on Twitter, to see if there are any potential hints from who he follows.
For studios (or people at studios) that he follows, I found the following that aren't owned by XGS:
Hypixel Studios (company twitter)
Telltale Games (company twitter)
Midnight Hub (through John Bernhardsson)
Iron Galaxy (through Adam Boyes)
Jackbox Games (through Mike Bilder)
Of course, he also follows multiple people/accounts from Blizzard and Nintendo, but those are obviously out of the question.
I don't really expect any of these to be potential acquisitions (aside from Iron Galaxy), but thought it was interesting nonetheless.