Thats pretty cool, i like the card going in the center of the cart design.
There have been a few versions of this before, starting with (i think) the
neo myth (more known for the n64 cart), and the more recent the
everdrive & super everdrive.
The neo myth is old news, and outdated hardware (came out in 2006ish?).
Kirk's everdrive is top-of-the-line. I fiddled with a neo myth and it was ok, but never got updates, and some games didn't work. I have an everdrive, and he is still releasing software & hardware updates (32x compatible, memory, ect).
I even got a guy from sega-16 to make me custom stickers & cover art for a genesis cartridge & box for the everdrive
(seen at the bottom here).