alt Hacker NewsDepends though what you pay for the one-time price. You can pay an offline version of the application (no extra costs afterwards), or a limited period of SaaS application updates (let's say 3 years).
I agree that paying a one time price and expecting continuos updates and new features is not reasonable.
For the majority of software I use, I don't really care about continuous upgrades and new features, as long as it works with the feature set I signed up for.
A great example for me is the Xodo app on Android. It's by far the best PDF editor that I've found on Android, particularly for annotating with a digital pen. Some features are locked. If I want to unlock them, it's $5 a month. I get nothing out of that which isn't already in the app. I'm happy to pay a one-off fee for the work the developers have done up to that point. I'm definitely not happy to add another $5 a month to my pile of subscriptions.
For me the boundary is this: (1) If I get something of value every month (e.g. use of a cloud server, or something which obviously needs regular updating like Netflix) -> subscription justified; (2) If I just want to use what I can already see in the app -> very unlikely I'll ever subscribe unless the product is absolutely essential to me and there are no competitors.
A good example of the latter is Skritter. I don't care about new functionality, but there literally isn't another app which can do what it does, so I pay the subscription.