OBJECTION!
RemoteJoy for the PSP did pretty well on this job. Only one game I played with RemoteJoy enabled had lags. And that game was Vice City Stories. Every other game worked fine.
But the 3DS lacks a USB-Port and therefore it won't be that easy to get anything on another screen... and Wi-Fi might be too slow (or you had to compress the data, which would actually mean a cpu drag).
Until someone really digs into that, I will stick to my $200+ Capture Card.^^