Sega's Facebook page features the above screenshot, of "Stick Canyon," an environment from the Saturn classic NiGHTS into Dreams. This could portend an HD re-release like we're seeing for Jet Set Radio and some Dreamcast games, or it could be a new track for Sonic and All-Stars Racing Transformed.
The screenshot itself doesn't appear to be new – identical-looking renders of the Stick Canyon location can be found on NiGHTS fansites from years ago. We've asked Sega for more information, but in the meantime, something NiGHTS-related is happening!