Looking forward to a future where all a politician’s quotes are on a blockchain, signed by their private key, and they chose to do so voluntarily out of fear of deep fakes.
"We verified the validity of our source's signature and vouch for it's authenticity"
- Journalist from a respected newsroom, when they choose to keep the source confidential. So it won't be better or worse than it is now: all about transitive reputation.
The unspoken threat to further denials is the risk that the source may go public, or if unauthorized, doxxing the person who recorded the video (assuming signatures have nonrepudiation)
That's a start! I think their video appearances should be like a car in NASCAR with permanently displayed logos superimposed from all the interests that have funded their rise.