Where do you check their subscription in order to cut off the service when they stop paying? One of the nice bits about local first is that there's no need for logins. Do you install security software in your local first app, which, typically, includes the code in a format that's fairly easy to bypass? Pirating desktop software was a big issue for companies. Are we going back to that horrible world?
So that kind of violates the principles of the local first software since you still need the cloud and license key in order to run the app. It also means more work for the developer, since they have no other reason to provide a server in most cases. It also means that they need to have logins which are not actually necessary for local first software and one of the benefits. Not so easy.