Some other factors would also prohibit this.
For example, playmore would have to manufacture these old, archaic cards with their old archaic cartridge counterparts. Not only that, but the neo geo cards were 2Kb large. they could maybe put a few megs of RAM on that thing for "cheap," or they could put a shitload of RAM on it for a lot, but neo carts are already goddamn expensive as it is.
Plus, i don't know how fast that PCMCIA slot really is, and how efficient it would be for it to be constantly writing to and reading from it.