Subscriptions are interesting. As a consumer I hate them, as a developer I also get/understand them. Ideally anything that has ongoing costs isn't part of the core app and there is a super stripped down version that is one time cost with no subscriptions. You want feature X, which has a recurring cost to the developer to keep alive, then pay up on a subscription. New major feature is introduced, new version of the app that is a separate purchase (if not using a subscription), maybe do 2 year chunks. Bugs of course should be fixed regardless, but otherwise think its entirely reasonable that without a subscription you are "feature locked" to what was there when you purchased.