If the app producer updates regularly with useful new content, I would be happy to consider a subscription. If the app sits dormant for more than a year at a time without useful updates, I do not want a subscription.
That might depend on what you get with the subscription. If it's useful enough to subscribe now, would it not still be useful a year from now, without an update? It only makes sense if it's no longer useful or outdated. There's a lot of "depends on..." there.