Nah, I find this cumbersome with too much work. I mean so what? the guy who paid for the file now has your file and he can upload it free anywhere... it never ends.
Another point, who verifies the file if it is protected tho? I mean, so suppose this... now is rA that has to trust *me* to upload a file and trust that I'm uploading something good as they don't have access to check it.
I think that as an author, all you have is to trust at certain point and do your own decision to upload a file or not. You end to have traffic (a lot) thx to rA hosting, and might end with some cash in your pockets, but really? someone has to verify the files lol.
Just keep the system like it is now.