close hardware wise in order for this to be possible?
Yes and no.
Yes, it's working. I made it. It's possible.
No, not really that close considered as systems, but surely close enough considered as late 70ies technology computers.
In the end those consoles/computers are no more than applications of a handful of processors and chipsets, which were cheaply obtainable around 1980.
I'm always getting amused about the pseudo-religious discussions, if a Commodore is evil and an Atari is so much better, or maybe the TRS is trash. Conceptually they are all the same. It's like car technology: If you disassemble a BMW and a Mercedes Benz, you'll find almost the same parts at the same places. A BMW steering wheel will work in a Mercedes Benz, if you solve the problem of attaching it.
Same here: 8 bit processors are connected to some expansion ports, with all their buses, looking for memory. Same voltage, more or less same clock-speeds, same memory access procedures. Like books, just with different words inside, but still books.
The Multi-cart now is heading for those early 8 bit home computers, which need memory space from 1k to 16k (future 32k) per game/program. Probably not Commodore and Atari, which really have countless and also very good solutions already out there, but some underdogs, with a more or less static game library. So, personally, I burn my eproms once and usualy don't have to change them anymore. (But I could anytime.)
I started the project roughly four years ago, when I was looking for a cartridge for my newly aquired Dragon computer and could not find a single one. When it was ready and working, I thought, maybe other people would like to have one, too, and offered my extra cartridges in the "Dragon Archive".