[martindevans]

What stops fraudulent reports?

e.g. 1. I pay you 1 BTC 2. Wait until I receive whatever I paid for 2. Now I tell you to send me 0.5BTC or else I'll report the entire 1BTC as ransom payment.

The blacklist is just a new and very powerful tool for additional fraud!

[nkrisc]

Presumably the registry could also have some mechanism of identifying those making the reports (maybe limited to insurance companies), and not just accept random reports of ransom payments. That makes it less ideal, sure, but it could help prevent the scenario you posed.