wow, that was some info...
edit; i wonder if they'll pass "the test" of that test rom...
It's always possible but I'd consider it highly unlikely for the M3. According to the author's notes(which I have no reason to doubt) the slot-1 protocol specifies a maximum random seek time that is much faster than anything NAND flash can do, only NOR flash, hard-printed ROMs and RAM can do it. If the M3 Real really is capable of running 1:1 without replacing any instructions to work around the slot-1 protocol, then the card is going to feature some sort of cache. Either it's going to be a small RAM cache to try to intelligently pre-fetch data, or a large RAM chip to hold the whole game. Otherwise if it's still a traditional controller + reader + NAND flash setup, then there doesn't seem to be any possible way for them to claim 100% compatibility.
The G6 will just be a M3 with the reader replaced with hard NAND flash chips. NOR isn't big enough(1Gbit max chip size), so there's just no other possibility.