I have heard of this type of mixing and matching on 29+ bikes - guys put a fat 26" front with a 29+ rear wheel so overall diameter is really close but kinda also opposite of what the OP is talking about, but same concept in as much as the wider, higher volume tire is in the front to take up trail chatter, etc. and the 29+ is in the rear as your motor.

Never ridden anything like this but I know of one guy who has a rigid bike setup like this who takes it down the A-line at Whistler. **shrugs**