This would require Roon to be able to search the metadata of all 100 million tracks on Tidal/Qobuz.
If it could, this would solve many other issues as well. However, it can’t do this on a little local computer, which is why the library / non-library distinction exists in the first place. Making it possible would probably require moving the Roon database into the cloud, where hardware is less limited.
You can find a selection of other similar limitations in this discussion: