I initially tried NPIV/virtual FC on my VM file server cluster but ran into endless issues, so I decided to move to shared VHDXs, which have been much more stable but with the caveat you pointed out. You can't expand the shared VHDX online, but since it
is SCSI-attached, you can hot-remove it and expand the disconnected VHDX.
I put together a powershell script that offlines the disk in the file server cluster, removes it from the VMs, expands the VHDX on the host cluster, adds the disk back to the VMs, then expands the volume. It isn't pretty, and I'm still ironing out kinks,
but it gets the downtime for the expansion to less than 5 minutes (especially if the shared VHDX is dynamic since you do not have to wait for the VHDX file expansion).
I have my fingers crossed that online shared-VHDX expansion is on the horizon in a future Server update.