Man - all these wheel sizes! So a 27.5+ is basically a 650b+ with what - just a chunkier tyre? I should have just bought a KTM!
650b+ is the correct name for the size. Its just the MTB industry wanted a term that riders could get their head around.
We already use 26" and 29" so the logic was put it in the middle, so they use 27.5".
The + bit means its wider, so half way to being a fat bike. So yes you could just stick a normal 650b/27.5" rim and therefore tyre on it. Or actually you could put a 700c/29" rim on it and then it would have the same outside circumference as the 650b+/27.5+ front wheel.
But if you want to keep the same tyre, you'll need to get a 27.5+/650b+ rim capable of coping with the extra width of the + size tyre. You can of course just run a normal width rim, but then the tyre profile will be a bit weird, because it'll be pinched more at the bottom.
This is quite a useful guide to the 4 different options on mountain bikes these days.
26" / 27.5" / 27.5"+ / 29" and Fat bike, which is actually a 26" wheel, just with a super wide rim / hub / tyre.
http://dirtragmag.com/the-wheel-size-explainer/