While it is not completely a sports thing but rather a management-related one, fans can still enjoy betting on who leaves next based on the team’s performance so in a way, it is somehow predictable. It may not be as sure as player transfers and whatnot but the grounds on which manager goes next is still there and gamblers just need to make sure that they hit the right predictions.
But yeah, the market for this will be very low though it’s a good idea still.
Now that the OP opened this up and if there are people who are interested on the same thing, maybe we can recommend it on some betting site? Or if there are betting sites who will read this thread, they might be the one who will add it but they must do an announcement about this new feature. I know a betting site who offers markets for any types of events including on the uncommon/unrealistic ones. It's called Futuur. Maybe we can also ping them about this.