I suppose the verifying node will itself need a copy of the file (or the part of the file it's verifying)? Then either the owner of the file will need his own node to store the files and verify (which somewhat defeats the purpose), or he will need to rely on other nodes to quiz each other. What incentive do they have for this, and in case of a conflict, who should be believed? What are the penalties for failure to verify?
The verifying node only needs a secure hash of the original (shares+ciphertext) for a file - a verify-cap is exactly this. To actually verify that whatever the other nodes are storing matches the original, all shares must be downloaded, hashed and the result compared with the verify-cap. There's no need for the sort of majority consensus protocol that I think you're suggesting.
Maybe there are already solutions for all of this, and if so it's great. But again, a fully monetized platform is a league of its own in the requirements for a comprehensive verification protocol. As I understand Tahoe-LAFS is not currently a fully monetized platform, so I have my doubts that such a verification protocol has been developed.
I can't think of any new requirements that monetization would impose upon the file verification protocol.