Not sure if vhdx falls under the same functionality as mounting a virtual disk to the host, but THAT functionality has been dropped in v17 per the release notes (and as I stated in other threads, including the one you linked here, that functionality has been horribly broken since 16.2.0... and the product manager admitted it will not be fixed). Major showstopper for me with my work, so my work machines are frozen at v16.1.2.
