"Zelda Universe" doesn't even make sense as a name for a MMO Zelda game, a better name would be something like "Legends of Hyrule" ...
With that said, who says an online Zelda game has to be massively multiplayer?
One thing that hasn't been explored much in the current generation is procedural content generation. In comparison to the cost of developing a next generation console the amount of R&D to make a massive breakthrough in procedural content generation should be very small; especially if you're working under the assumption that it is a hybrid system, and large parts of the content would still be created by talented developers. To put a rough estimate on it, developing the technology might be in the $10 to $50 Million range; and it there would still be a lot of additional money on top of that to create the "Zelda" specific content.
The net effect of this could be a "sandbox" Zelda game where everyone's world was significantly different, with different dungeons, and what not; and the world could potentially reflect the changes made to it in the way that was (over)promised by Peter Molyneux a decade ago. An interesting way to play a game like this would be to allow people to play online together potentially using one of their own worlds, or possibly on a game world that they alone share. As a result the game would not be "massively" multiplayer because it was simply a multiplayer game, but it would still be a unique multiplayer game that no one has played anything like before.
