I decided my next e-bike would have a bafang BBS02 mid-drive, and the donor would be my old Diamondback mountain bike, but I recently picked up a cheap fat tire bike. A fat tire bike is an good mid drive candidate, because I don't have to mess around with the rims and tires, but the only mid drive that fits the fatbike BB is the Bafang HD, which has more power than I want, although the most recent user reviews say it doesn't have the power that the top posters on endless-sphere crave.
I've ordered two small geared hub motors instead to attempt a 2WD fatbike for slow speed winter riding in snow . One comes with a 190mm dropout to fit the rear and is supposed to have a rim. The other is a bare motor for the front so I ordered a rim and will learn how to lace it. Total cost so far is more than what a BBS02 would have cost me, but less than the HD which I didn't want anyway.
So my BBS02 build will be deferred. Maybe next summer. The BBS02 will be more than fast enough for me, and I know how to shift and keep a motor happy. That's one thing about the US market. We're a nation that drives cars with big engines and automatic transmissions. and most people just don't understand gears. If you're willing to help the motor out with pedalling, any bike can climb most hills.