Agenda notes app has elegantly solved this. Pay once and permanently unlock all current features. If a new release has a feature you want, you can purchase again.

It's more work for the developer but they did a great write up on how they built this capability: https://medium.com/@drewmccormack/a-cash-cow-is-on-the-agend...

Hmmh, on its own its not enough, I think. Just read through the post, and there is no trial of expensive features in their setup, just a set of free features to begin with. But it seems that Apple allows these days to trial features, as long as your app remains usable and useful without them.

Well, not apple to be fair. Developers are free to set their prices to whatever; it just so happens some developers set their prices to $0.99 and set that as the expectation

It's a race to the bottom. There's always somebody willing to go lower and the app store doesn't give you much room to stand out. Before I quit I had users complaining my app was overpriced at $1.