Does Wii Fit U support two balance boards simultaneously?

Wii Fit U does not support the use of multiple balance boards simultaneously.

The way the Balance board works, is that it emulates wiimotes, and uses 2 of the four channels for wiimotes. (I believe it's hardcoded to use channels 3 and 4, so that would make using 2 balance boards impossible)

So technically, the wii does have the capability to listen two balance boards, but none of the software supports it, so having more than one is superfluous.

Having said that, Wii Fit, and Wii Fit U both allow for multiple people to use it, just not simultaneously. Our family all gets measured at the same time. The kids like watching the parents get measured and play the games, as well as playing the games themselves.

Based upon a look at the available games, there does not appear to be any game that has a simultaneous multi-player mode.

In fact, Nintendo doesn't even mention multiplayer modes for any of the new games. It is likely they have them, since this was a feature of Wii Fit Plus (by taking turns), but there is no mention made.

Just like Wii Fit Plus, it does support multiple users. Each individual user can have their own fitness track, plan, games, etc. But, I do not see anything showing that multiple users can be competing (or cooperating) on-screen at the same time.

Source: http://wiifitu.nintendo.com