Well, tbh the OG thing is a big thing because it's Goto Maki. It would never be as pushed if it wasn't for her, and it makes perfect sense.
I doubt MM will be in the background though. They'll most likely get to perform Tokisora or something, it's not like MM are irrelevant in Jpop anymore. If they weren't gonna perform solo, they'd be listed as a united act with MM OG. "MM OG and MM '14" etc.