I can’t seem to find the MSDC in sys-usb. Do non-usb devices like micro SD cards appear in sys-usb? Running sudo fdisk -l doesn’t show the MSDC, and there’s no /dev/xvdi or the like.
I might try overwriting the () device and see if that works.
Edit: it seems that attaching () to a VM also attaches the boot and rootfs partitions to that VM, which may be why those partitions disappear from dom0.