They will need to have a card with 2 gigabytes of flash memory otherwise its not going to be able to fit the Europe version of "Super Street Fighter IV - 3D Edition".
The RomFS size of that game is about 1.63gib (and that size is not counting the ExeFS and headers)
since 3DS carts are sized in powers of 2 (256mib, 512mib, 1024mib, 2048mib) it will get rounded up to 2 gigabytes (or 2048 mb)
From the Header of the "Super Street Fighter IV - 3D Edition" ROM...
Code:
OFFSET SIZE DESCRIPTION
0x1B0 4 RomFS offset, in media units
911A0000 (00001A91 x 0200 = 00352200) = 3,482,112 bytes
0x1B4 4 RomFS size, in media units
80113300 (00331180 x 0200 = 66230000) = 1,713,569,792 bytes
0x1B8 4 RomFS hash region size, in media units
02000000 (00000002 x 0200 = 00000400) = 1024 bytes
and the Europe version of 'Rayman 3D' is 256mib (RomFS size is 197,222,400 bytes, when rounded up its 256 megabytes)
I guess they might do what the GBA flashcarts used to do and have different card sizes, like 256mib 512mib 1024mib and 2048mib for different prices.
that would be better then to only have one size available (say 2gb), instead of using an entire 2gib cart to flash a small 256mib game on it you could use a 256mib/512mib card instead.
I know I would buy 2 cards (depending on price), a small one (512mib) and a big one (2048mib) so I don't have to re-flash the card when I want to switch games.
Not sure if there is much difference in price between a 256mib flash chip and a 2gib flash chip but if there was, it could make the cards cheaper.
Known sizes of 3DS Roms so far:
Super Street Fighter IV - 3D Edition (Europe) = 2048mib (2gib)
Rayman 3D (Europe) = 256mib
Tom Clancy's Ghost Recon: Shadow Wars (Europe) = 256mib
Super Monkey Ball 3D (Europe) = 256mib
The Sims 3 (Europe) = 256mib
Lego Star Wars III: The Clone Wars (Europe) = 512mib
Ridge Racer 3D (Europe) = 1024mib (1gib)
All this is probably useless info, but at least people will have an idea of the size of the games...