I spotted the AmpDrive AD510 that looks like a nice board, the main carrier is open source here but it’s designed for a proprietary BD1D50 module.
It occurred to me that if someone made an opensource STMxx version of the MCU module then you’d have a relatively pro open hardware system for comparatively little effort.
They did seem in-principle up for selling the carrier without the STMxx however all their existing stock is pre-soldered, so it would be a case of de-soldering their existing board, or fabricating to do any testing.