This simple non-blockchain protocol is just as good:

1. Hacker encrypts victim's data with 11 segment keys

2. Hacker gives victim 1 segment key as a free sample and communicates the ransom price

3. Victim pays 10% of the ransom price. Hacker sends another segment key.

4. Repeat 10 times.

Like you already pointed out, it's easy to trust the hacker because the hacker isn't much of an adversary in this context. They have no reason *not* to help the victim decrypt their data.

So I don't agree that smart contracts will have a noticeable effect on the randomware landscape. (Though of course if we're just talking about cryptocurrency, like if governments allow untraceable crypto like Monero to grow in popularity, then that will continue to have a large effect on the ransomware landscape.)