Yeah! My understanding is that so long as you can encode Y definitely happened as a preimage, you can use Lightning to incentivize John to do Y.

I was asking about an HTLC based storage system on Twitter and xraid replied with this project https://github.com/joostjager/deadmensbutton.

Naively, for something like storage you need some kind of watchtower like thing periodically sending incentives John. But for short duration work you can probably achieve it quite elegantly.