This is internally possible, but not exposed to users yet. That’s how we run our remote builders.
Not setting any service on your app shouldn’t assign it an IP.
If you set all the regions you’d allow your app to run in, it would schedule it anywhere from that list whenever you start it.
The only thing missing is exposing the “ephemeral” kind of app to users. I can take a look at that. Let me get back to you.