What is the most useless app that you have seen being given as a subscription?
For me, I tried a 'minimalist' launcher app for Android that had a 7 day trial or something and they had a yearly subscription based model for it. I was aghast. I would literally expect the app to blow my mind and do everything one can assume to go that way. In a world, where Nova Launcher (Yes, I know it has been acquired by Branch folks but it still is a sturdy one) or Niagara exist plus many alternatives including minimalist ones on F Droid, the dev must be releasing revolutionary stuff to factor in a subscription service.
Second, is a controversial choice, since it's free tier is quite good and people like it so much. But, Pocketcasts. I checked it's yearly price the other day, and boy, in my country, I can subscribe to Google Play Pass, YouTube Premium and Spotify and still have money left before I hit the ceiling what Pocketcasts is asking for paid upgrade.
Also, what are your views on one time purchase vs subscriptions? Personally, I find it much easier to purchase, if it's good enough even if it was piratable, something if it is a one time purchase rather than repetitive.
I'm going to go with the unpopular opinion, that all apps should have the subscription support model.
Especially open source apps!
Ideally the code is open, and under GPL or a GPL.
Unless you have a device completely disconnected from the internet, there needs to be constant development, to update libraries, to get security updates, to fix rare but critical bugs. Nobody, and I mean nobody, should be running a binary that never gets updates from 10 years ago, on a device connected to the internet.
I seen a variety of approaches to supporting app development, I think a lot of the pricing is targeted towards the richest people, ignoring the vast majority of the world. For open source apps having the app itself with a nag screen, or a supported version of the app that is just a recurring donation maybe a dollar a month.
All that being said, when the subscription ends, the app should still work at the last version, and the user just assumes the risk of running older software un maintained.
(I'm aware there's ways to mitigate the risk of unmaintained software, running in a very highly protected VM for example...)
Most users can't name a single reason why their programs should update.
They don't see risks in running unmaintained software. The developer does. I could get behind your all-subscriptions ideal, but if the user terminates the subscripition, he should be made unable to keep using the software. Hence why this cannot be the norm with Free software.
If the app doesn't have network access, though, the OS sandbox should be more than sufficient to keep it secure.
A calculator app should be safe to run without updates at least until the OS APIs undergo a breaking changes (which should take several years at least).