For every couple year major versions (with decently advanced notice it's coming and/or a recency allowance) I think it's fair to charge anew but for minor improvements over the lifecycle of a major version I think it's fair to want to buy everything that will come in the major version up front if you're making a one time purchase. Tons of software is this way from Sublime to Windows to ZBrush to an absolute crapload of games. In this model a one time purchase is seen more as an alternative to holding a subscription over the lifetime rather than the intent to forego any future features or enhancements out of interest of the exact current feature set being all you'll ever want. There is also the "in-between model" e.g. IntelliJ where you get the current version + a period of updates and you can either stay with where it ends at that period or pay a smaller amount for more updates.
I'm not sure which group the Halide changes mentioned above fell into but just on the general topic I think it's a fair expectation.
They do something which is "common" in Apple-land (Dash for MacOS does this, a Twitter client did this as well, over and over): They get the same app, add some features, call it v2, launch as a new app and remove v1 from the store.
They don't "give" you the new version. They take away the app you paid "once", and provide you with a version with an expire date. So you have no choice. You either pay them, again, or lose access to the v2 (subscription based) app.
I don't mind paying for good software, I even think Hallide is worth $60. But I won't make the same mistake again. So best of luck Lux! I really wish you all the success. If you treat your customers right this time.
That is "forever updates" = no but "take away what you had" also = no. It was a period of updates with a dropoff date of where you left off. This lines up with my expectations of a one time purchase in that I'm not expecting 50 years of feature updates when buying software just because they haven't went out of business yet I'm just expecting I keep the feature access I have at the end, which is what these posts from many different folks are all claiming.
I'm not sure which group the Halide changes mentioned above fell into but just on the general topic I think it's a fair expectation.