Personally I don't see the difference between this and submodules. Repo stores the information in xml files, vdm stores it in yaml files and git submodules in the git database. I don't really care.
The real headache for me is the trouble of traceability vs ease of use. You need to specify your dependencies with a sha1 to have traceable SLSA compliant builds, but that also means that you'll need to update all superrepos once a submodule is updated. Gerrit has support for this, but it's not atomic, and what about CI? What about CI that fails?