Paying for syncing with Obsidian is not necessary. You can use a free version of Resilio sync to sync folders across devices. Roam is dangerous, who wants there notes hosted? Remote does offer a local only version with their desktop app.
I would vote for a different business model Offer an annual fee for buying that yearsā new features. You get to keep those for life. You can pay the next year if you want to support further development and/or because you like the new features they are building. In that way, the developers have an incentive to listen to their users. $6 is a fair price. Agenda (agenda.com) has this business model as does Tinderbox (Eastgate.com). I would pay for $10 a month or a discounted $100 for annual charged at once. Point is, you always retain what you paid for, nothing will ever been taken away. Why is this more fair? Because in the year that you paid, you supported the development. At the same time you are not locked in. That is really a user-oriented as well as a developer oriented business model.