Update: In the latest title update, the Star Wars Clone Trooper image has been removed from common_d9.rkv. The icons and banners remain the same.
I happened to look in the Game Room directory and see a big resource file earlier today. I figured that there might be some images in it that could give clues about future content, and there was!
First I checked for PNG headers files using a hex editor, then I used this Perl script to extract them.
In the image below, you can see that it contains a number of unused achievement icons (is that one with Pac-Man, Quick Man, and Air Man an achievement for “extra mans”?), new content pack banners, and strangely a picture of Star Wars clone troopers. Maybe that’ll be used to announce the original Atari Star Wars arcade game.
Check it out: (click for full size)
I’ll update if I dig anything else out of C:\Program Files (x86)\Microsoft Games\Game Room\common_d9.rkv.