When detecting a Pikmin save game, SSB:M unlocked an Olimar/Pikmin trophy, if memory serves.
I had hoped that more GameCube games would unlock more trophies, but alas, that wasn't the case. (I don't remember how the Japanese got the Caped Mario & Yoshi and "Zero Helmet Samus" trophies but I think they were unlockable - yet us North Americans got the shaft there, and no Devil World devil-guy (Takagon or something?), either.)
I would like for SSB:B to have this feature, especially if I'm going to be buying most first-party Nintendo games anyway. Besides saves, maybe it could also detect which Virtual Console games I've bought.
For future games to unlock new trophies that weren't conceived of at the time of release, that would require "trophy data" within the other save files themselves (which might add size, unless they first detected if an SSB:B file was there to begin with), or an online connection (which there is now) and a hard drive might be handy, too (which there also is).
I suppose there could be a trophy collection thing in the Wii OS itself, and not in SSB:B necessarily. Then the trophies could remain online and based on your accomplishments/downloads/games played/etc. it could just load up a trophy each time you want to view them. I guess Xbox Live has something that tracks your accomplishments but virtual trophies in the likenesses of Nintendo characters would have to beat whatever they've got.
Or is this a stupid idea that only other people like me with a need to collect Nintendo stuff would even enjoy?