Yes this is a nightmare scenario, I would not be able to support products sold by anyone using this model. Unfortunately I think there’s not a good way to do subscription services that don’t lead to this, because it’s a foot-in-the-door to worse subscription models and the temptation is there to go the adobe route if you already have a subscription-based service in place.
Personally, I think the older software model was better - the way it used to work was really not a subscription service as you describe (for a lot of softwares anyways) but instead you would have to buy newer versions of the software, and those came with time-limited support. E.g., You bought Photoshop 10…well, when it’s out of date if you want CS2, you have to re-buy it.