That idea just came to me today, and I'm now pretty much 100% sure it will be built sooner or later.

There's no part of it that is actually HARD, technologically speaking.

You don't need radio to run down a person, just a camera and some little AI object recognition and steering logic.

Anti-tamper systems are obviously pretty simple.

You don't need reliable radio to check a txn on the blockchain, they provide the data to you (like with a phone app or something), and you can validate it offline by checking that the proof of work is there.

The person who drops it has very little risk of getting caught, just throw it in a ditch, few days later it takes off and grabs someone...

If you can build something for 1k and it makes 1mn in ransom, that's an extremely lucrative proposition...