a couple years back I used to run into PJ from Norco on the local hills and he was shredding a cross breed 29/27.5 combo , not sure what frame it was , may have been the Sight .
The more I think about it, the more I'm tempted by this 29er front, 27.5 rear 'Frankenbike' idea. I even totally geeked out this weekend and started building a excel spreadsheet of medium frame geometries to try and get a better idea of which options would work best while still maintaining 160mm of 29er boost fork travel. High on my list is the Santa Cruz Nomad but I'll need to demo one to see how they pedal since there seems to be a wide range of opinions about this. Either the 29er or 650b Specialized Enduros would probably also work well in this arrangement but I'm not as keen on these as the rear suspension linkage design doesn't seem as dialed to me.
I demo'd a Transition Patrol Carbon this weekend and loved the rear suspension but I don't think this would be a great candidate for my Frankenbike unless I reduce fork travel to 140mm on the 29er fork and / or install a 2 degree headset cup in reverse to steepen the head angle with the longer axle to crown length. Unfortunately I didn't get a chance to try a Smuggler but I think that was still a long shot as a 29er bike option for me due to its short travel.