I've heard it's 8 gig this time around but I don't believe this has been confirmed.
It also looks like M2 has added some features to some of the games included on this mini. Not only the usual quality-of-life features at a system level - like save states, rewind, etc - but unique features per game. Supposedly, Phantasy Star II, Outrun, Hellfire, and Rainbow Islands all have some enhancements. Perhaps others as well.
So far, I've kept all of my minis stock out-of-the-box - the exception being the Playstation Classic. You really have no choice but to hack that thing to bring it up to par with the others.
I'm hoping - once the chip shortage is under control - Sega decides to revisit this mini and make a traditional push at retail. Maybe by next Christmas or whenever. I've had several casual gaming friends and family members who've shown interest in these mini consoles, purchased the first Genesis mini, and would probably pick this one up as well. If they see it sitting on a retail shelf somewhere.
I also hope Sega makes this a trend. I'd love to see a Genesis Mini 3 with another round of Genesis and Sega CD games. Hopefully Lunar/Popful Mail licensing with Victor Ireland/Working Designs will be resolved the next time around. And maybe throw in some Game Gear and Sega Master System classics as well.