Let's cut a long story short: MoPi should work fine with the Model B Plus Pi announced yesterday.
The Model B+ is an evolution on the original Model B; it looks like this:
From a mobile power point of view the B+ will perform a bit better than the B — they're replaced the rather wasteful LDO regulator of the original with a switched-mode supply, and with the revamp and extension of the USB subsystem they've also improved power handling there.
I've a couple of Model B+ boards and will post some pics in a few days...
So don't be afraid to pick up a Model B+ if you fancy one! It looks like a great addition to the Pi stable.