Please note that this is just speculation, rumor, and personal desire.
So Majora's Mask came out last week, I've not yet bought my copy (hopefully I'll pick it up tomorrow, or I might start Mike Tyson'ing people), but that hasn't stopped me from looking forward to the next potential Zelda entry on our neat little handhelds.
In case you can't guess from the above image, many personal dream is that Twilight Princess will make the jump. I believe without a doubt that the system could handle the game, it's a damn powerful machine, really. This would put my top 3 Zelda games on one system, what's not to love?
No indication or solid word leads me to believe this will happen, but hell, I don't see why Nintendo wouldn't port it, it sold very well (actually THE BEST SELLING* with at least 8.5 million sales), and got critical acclaim (9.5, 9.5, 5/5, the LOWEST score it got was 8.8/10)
Why would Nintendo not want more money? If they have any business sense, it's a no brainer, and Nintendo is pretty good about heading their fans.
*according to vgsales