A lot of times TM's amount to nothing, but it's hard to ignore the timing of this news. If it is something, more likely than anything, it's just new sw support for the Balance Board , especially considering the fact, that it's called Wii Fit+ and not Balance Board+. The gameplay could combine Balance Board and M+ controls. That could definitely make for a successful follow-up and boost HW for both peripherals. Not to mention, encouraging developers to make titles that use both, in conjunction.
I doubt it, but it could also be for their next system, seeing how Ninty often TM's peripheral related stuff, further in advance. Maybe, it's an add-on peripheral that works with the BB, like how M+ works with Wii Remote. I guess, will just have to wait for an official statement, to know for sure.