On my 2018 Levo Carbon I fit a 29 x 40i Derby rim to match my front wheel, both with 2.6 tires. The rear 29 x 2.6 tire barely clears the swingarm's lower stays bridge with about 4mm at best, less than ideal and makes it not possible to use a rear "hugger" type fender to protect the motor area mounting the hugger fender (using a small front fender) under the swingarm's cross bridges.
The 29er in the rear is slightly smoother riding over rough trail. A far smoother improvement was going to a coil rear shock.
A very close side by side measurement of battery usage with my 29ers x 2.6 tire vs 27.5 on my buddy's same model Levo with stock 27.5 x 2.8 tires, with same tire model on both bikes and same battery power settings, found no more than about 1~2% better battery percentage use with the more efficient rolling 29er rear wheels over a long 30+ mile ride distance.
I prefer the 2018 Levo's handling with the 29 x 2.6 front with 27.5 x 2.8 rear tire "mullet" or "mixer" style. And fender clearance is no problem.