It's really all just down to my own personal preference Dom.
Coming from DJ and old skool DH background I'm more of a #264LYF type of rider. Sort of the opposite of a lot of new skool enduro/trail rider with their super long super stable (but less nimble) bikes and riding styles
I'm 5'11" so not exactly tall and just don't get on with 29er mtbs at all. I can ride them (possibly actually faster in many situations) but I just can't stand the lean in the higher axle and larger diameter wheels gives when turning/changing direction. It's far more of an enjoyment preference than anything to do with the larger wheels performance in covering ground fast for me.
I'd also far rather have a mismatch in suspension travel (in favour of more up front) over less fork travel and a larger diameter front wheel. this also allows more scope for finetuning of ride height via suspension settings.
We don't ride "Moto" bikes (proper engine ones). they'd actually be worse for the sort of riding I tend to do and aren't designed to. I've always run a grippier front tyre up front. (since the early days of BMX) which means either a softer compound, more aggressive tread, or larger volume (or a combination of the 3) front tyre. The 29 front, 27.5+ rear idea goes against this thinking some what.
plus, as I said earlier in the thread. I can lower and slacken the bike by doing this gaining stability without sacrificing nimbleness
I hope this helps you understand slightly better where I'm coming from
Before anyone brings up Maes (#no_spoilers

). He wasn't using a rear plus tyre
He is making the most out of 27.5's smaller diameter for pretty much the same reasons I love 26" in the rear