And Octopus (perhaps others, only I'm aware of) even offers an hourly tracker plan ('Agile'), with an API.

Also, due to Ofgem regulatory requirement all plans have a cap, so this couldn't happen. (It's not capped cheap of course, but it's not going to cost thousands/month. With Octopus specifically it translates to 35p/kWh cap on its variable rate plans, ~double recently typical prices.)