That may be the case for M500, but not for M510 and even less for M600. A lot people love tinkering and Shimano is closed. However frames that fit Bafang drives are often trash when it comes to geometry and quality. Other reason might be that one may convert his old Shimano bike sitting in the...
Working on it. Not yet, but yes my intention is to make the existing batteries work with Bafang. However you won't reach as much range and power as you'd with a custom build pack.
2020 I bought myself a Haibike XDURO FullSeven S (2017) and converted it from Bosch to a Bafang G510 with custom Innotrace X1 controller. It's a beast and theoretically capable of 3500W raw power. Had to install a Rohloff Speedhub, to avoid changing cassettes every 2 weeks!!
Still want to...