Personally I'm of the mind that probably the best bike to convert would be an old name brand steel frame mountain bike with V-brake mounts on the rear. XD rear hub with rear V-brakes and a seven speed spool so everthing fits nicely in the rear and then put a modern front suspension fork on it with front disk brake. Rear V-brakes, front disk brake combo hard tail with good modern front suspension. Modern click shifter brake handle combo units on the bars (new old stock 7x3 Shimano still available online) and call it good.

Sounds like you and I have similar ideas as far as this motor. I really don't need another e-bike myself since I've already got a dozen or so bikes half or so of them e-bikes but I've just got an itch to try out this new XD two speed hub for myself. Been on my mind so when I saw your post I thought I'd point it out to you as well.