My understanding is that we have quietly enabled Pilot for everyone. If your use the machine API and you include containers in your request per the blog post I linked, you should be able to run systemd as pid 1. If this is not the case, let me know and I’ll find out more.
As to the rest, I’ll be honest and say that I don’t know what Discoverable GPT is or, why it would be useful, or if it could work on fly; I’m just responding to say that if running systemd as pid 1 was the roadblock, there now is a way to do exactly that.