I think it could be a fine independent product, but they'll need to be be bit more hands-on and responsive than usual to make it effective.
Biggest problem I see right now: every time you leave a wave and return, the state of the wave is not saved. so if you have selected 'hide inline replies' in order to have a high level view of a wave with multiple sub-threads, the next time you access it all the subthreads are expanded again, and it's not immediately obvious which changes have taken place.
This may be OK for small teams of friends or single-topic discussions, but is severely limiting for hub & spoke discussion models, an area in which it otherwise has great potential.
Also, I'm not too sure about the 'username@googlewave.com'. It seems a little perverse to create a parallel namespace, although perhaps the purpose of this is to avoid a repeat of the buzz launch where people found themselves signed up to something without even knowing what it was.
I wonder if they will still try to push wave as an independent product or it will just die slowly in the background without anyone noticing.