It wouldn't make any difference at this point, except to give users more options and price flexibility on their storage solutions.
The real problem is that Nintendo still has tons of restrictions on how games access the SD card, and on what kinds of data can be delegated to the SD card.
Installs are nowhere near happening, as Nintendo has no system for online authentication. As Pale noted, you still need the disc on 360 -- installing just helps with load times and drive noise. On the PS3, there is no "optional install" feature. Some games require an installation to keep down load times, but you still need the disc because many assets are still loaded optically. Among all three consoles, the only legitimate games you can play without a disc are ones that are downloaded to begin with. (The closest things to an exception are the game-specific channels installed from Wii games like Mario Kart and Wii Fit.)