Wouldn't block hashes solve revocation, as they can't be faked like timestamps can be faked? 

As in: "I hereby revoke your writing permission from this point onward: 00000000000000000003509af203f00a74cada8024e017982fe9c499751f36de" 

https://mempool.space/block/00000000000000000003509af203f00a74cada8024e017982fe9c499751f36de