I could _maybe, maybe_ see self-hosted GitHub runners inside of VMs running on developer machines. The VMs would have to be re-created after every request however.

I don't think this is a great idea, however, as now CI is dependent on my flaky laptop's wifi/internet connection/IP address, has the potential to be contaminated by something running on my machine, build logs can be modified, environment shape/architectures are all different and can't be easily controlled, I now have access to all of the CI secrets and can impersonate the CI, etc.