Seconded. Perhaps an external USB port that would allow flashing of some fast SRAM or something like that?
Yes that would be I guess expensive but damn cool...something like the supereverdrive but with flash for a whole romset..?
...given the relatively well-known content (read: no need to add games in the future) , maybe it would be cheaper having the user burning the flash write-once chips autonomusly (i.e. chinese sites,) and simply put them in the empty socket in the cart....that way there is no need for the re-writable flash... (of course, dealing with corrupted flash from the chinese company is another discussion...)
Rcantor, "switching" between flash banks already written allows to jump from game to game immediately, an SD-like storage would force to write a game at time to such flash (I'm simplifying) with long waiting time and limited choice, like few games at once.
In short, the multi-cart concept requires the games to be selectable and playable (SRAM/flash), while everdrive allows to load (from SD) a game at once...like a copier back in the times... problem is for neogeo it would take tenth of minutes for bigger games....I personally like instead the "MVS-1" concept as envisioned by Raz.