Hard tails are easiest to convert really. Even easier if weight isn't a huge deal. Generally the BBxx motors will work okay. There are some other companies I think doing similar stuff now.
Or there are some reasonably priced frames with integrated Bafang drives out now too.
I'm trying to build something as light as the lightest factory full suspension ebikes ~45# and easily convertible back to just pedals. The Lightest and Revel (yes from OR) are basically the only options except maybe CYC but that seems to have issues (although maybe just because of the power level).
Definitely lots of time to spend money I don't have.