Why would one sell permanent ownership of a networked product? I've been seeing the rise of "lifetime" subscription levels (pay once) for SaaS products, but I'm curious as to what the actual long-term economics of it are.
If your cost of operations is not a one-time cost per user, I don't see how you can avoid a subscription model.
You wouldn't. Maybe TFA has an extreme interpretation of local-first, but the entire point of the article is eliminating the last vendor-controlled server from certain kinds of apps so that the user can own the software forever.
Obviously this doesn't work for all apps, and it sounds like OP may have one that needs some form of network component. In that case what you propose would work very well.