Virtual Console games from your 2 or 4 gig SD card sounds like a very plausible one, the truth is very different.
See, the data access speeds for the SD card are extremely slow, apparently. That's why it takes awhile (in the case of the TG16 CD-ROM and NeoGeo, forever) to load the data onto and from there. So, if you tried to play a game directly from the card, it would be an atrocious affair. Shame, really, because the chore of copying and erasing all of this data can be a real pain.
Of course, this is all unconfirmed at this point, considering the "news" comes from a random post on an internet forum. So, if you have a grain or two of salt lying around, be sure to take this tidbit with them.
[Via Go Nintendo and Nintendo Everything]