We know from the economics of scams that any social engineering attack that is cheap enough to do and can be made plausibly urgent enough to get people to not question it can be hugely profitable. Deepfake blackmail has the potential to check off both of these boxes:

1. Porn adds plausible urgency by defaming the victim. People will really, really do anything to avoid being associated with the porn business, as can be seen by how many copyright trolls specifically troll with porn as opposed to other copyrighted works.

2. It is getting cheaper to train deepfake models and public social media photography provides a large repository of images that could be used to generate face swaps.

Right now I haven't heard of this kind of blackmail actually happening yet. This is primarily because deepfakes still require manual labor to cut out large numbers of faces, and the training process takes a while.

However, these are both surmountable problems.

Ransomware has been a technically possible form of malware for some time, but the problem was getting money back to the thief in a way that was difficult to trace. The kinds of scams that target technically illiterate users use money mules, but that relies on the unwillingness of the criminal justice system to prosecute the kinds of crimes that hurt the weakest in society. Bitcoin made ransomware a lot less risky of a crime, to the point where a lot of criminals targeted large businesses that would ordinarily be protected by the law.

The only thing keeping it from being profitable to deepfake all of Facebook into a bunch of porn is that it would be expensive to do so. However, that's purely a technical problem, and the thing we know about technology is that it almost always gets cheaper over time.

[0] Tom Scott was actually going to do a speculative fiction video about this exact hypothetical... before the whole deepfake porn thing took off and spooked him out of it.