I think the world of Zelda could make for a great MMORPG/MMOA/A (action/adventure). Especially the Wind Waker world... a bunch of boat sailing around :-D except there would have to be bigger islands, cuz interacting with other people on boats would be kind of boring, but it's still a cool picture. I think it would be cool if the sequel, you know, now that everything is gone except for Outset Island, would take place as an MMORPG, with customisable characters, and the premise basically would be explore and discover a new world, (of course there would be some cool mysterious plot or something). If it would be an MMORPG, it would have to have experience points, otherwise there's no point to a MMORPG.
Or not...
I'd really like to see an MMORPG take full advantage of how freaking COOL they could make it be. A gigantic, mysterious, world, some parts sunny with people running everywhere, some parts misty with just you and a few party-members. Ragnarok Online came close... the IDEA of PSO came pretty close (just watch that opening video... the whole mist and trees thing and the different characters "HUmar... RAbo..." or whatever, coupled with the music, and then that climax at the end only marked by an intense swellling of the strings).
But this was about a Zelda RPG, right? Yeah, cool idea.