It would be great if Roon would let me import more metadata and open up its custom fields external taggers.
To be honest: I can’t see Roon to ever evolve into a curation friendly tool. Its approach to do everything automatically is a cool idea and it seems for the vast majority of Roon users this works just fine. Personally, I think it’s far from perfect for a few (a very notable few) of my use cases and if nothing significantly changes regarding metadata quality I’m not hopeful that my experience will improve. And somehow I doubt rovi will adjust to my wishes …
My advice to everybody who wants to curate would be: do it outside of Roon but do it with metadata - not with folders. 
One other point: Roon customers do actually pay for the “lock-in” - the metadata service Roon provides is an essential part of the product. If I remember it right, it’s not even the software but the metadata service one subscribes to (yearly or for life). Why should we be able to take that with us should we move on? Even so I wouldn’t mind. 