My apologies if regular members are not supposed to comment on threads in this section.
I think a massive issue with this would be needing to maintain said tags. Licenses come and go from various streaming services, so having it tagged as being there and it being removed later down the road would be annoying to users. I'm not sure there's any simple way of tagging and maintaining such a feature and could become extremely tedious, unless there were a way to tie into other sites, scan if the show exists there and make that available.