It's not append-only. No one is suggesting that any new service must only pull keys from GitHub once and then it never changes. GitHub is just a convenient sour

It's not append-only. No one is suggesting that any new service must only pull keys from GitHub once and then it never changes. GitHub is just a convenient source to bootstrap from. You might need to go into your new service (possibly through another factor like physical access or web admin) and manually revoke compromised keys. I just don't think any of this is a reason to have a separate key for each service you use, that still seems rather unnecessary.