the swapfile would be impossible to use for opera browser.
a microSD can already barely keep up with the reading/writing of roms.
adding ram reading/writing to that would make it so slow it would instantly freeze.
I think Nintendo should consider releasing some kind of co-processor/ram pack for slot 2, kind of like how some n64 games needed the ram expansion pack for enhanced graphics. Hell, may be they can just use the opera browser ram as an option for improved graphics in new games. 4 MBs ram ain't so flash these days.
If I remember rightly, some N64 games did need the RAM expansion for graphics, whilst some needed it to work in the first place. However, some games (like SSB) slowed down to crap and occaisionally crashed completely when it was left in. There's probably a similar problem with NDS.