Needed for lvm2 USE=vdo
Kernel part (kvdo) has been merged into mainline for 6.9: https://www.phoronix.com/news/DM-VDO-Merged-Linux-6.9 So the userspace part (and maybe a change to sys-fs/lvm2 to optionally depend on it and >=virtual-sources-SomeVersion) would be the only things missing.