I'm already banned from publishing Android apps through Google, but apart from that, what would stop me making a server you can upload any app to and sign it with my certificate?
That could actually be done solely on the device. You can develop an app to sign arbitrary APKs with users' own hobbyist certificate. Lucky Patcher have done that for a decade.
I could even just give out my certificate and private key (if I'm allowed to have one). It's not like I need it to be private. Google would probably blacklist the certificate and then we get to sue Google based on the fact they said doing this would allow the app to work, but they didn't follow through with what they said.