The model is the "old school" model for software sales.
The first version you sell to a user at full price and offer a discount for upgrading (something like 40% off). It lets the customer pick when they feel the value prop is worth the cost and lets you offer a loyalty incentive to the user.
Right now the choice is "keep paying for it to keep working" or "fully price for every upgrade".
I don’t exactly remember how it went but ~5 years ago Goodnotes 5 came out and they offered a “bundle” of Goodnotes 4 and 5 together at the same price of Goodnotes 5. Maybe owners of version 4 had some kind of discount on the bundle because they already owned half of it?
Bundles can be used for upgrade pricing, you put the new version up for full price (ie. $20) and and a bundle with the new and old version (ie $30, for a 50% discount on it) for those who own the old version. When you buy a bundle you don't pay for the one you own.
Are there any examples of apps that do that? As a consumer, I haven't ever heard of an app that offers this (e.g. goodnotes, LiquidText, MarginNote, Audulus and Things have new major releases and don't seem to do this)
Couple of the old school macOS dev houses tried this once this hack became visible and little birdies said the hack WAI. (ex. OmniGroup)
Since then, people have backed off.
If you're going to this much work to help users workaround Apple nonsense, you really care about helping them save money, and the support + refund costs of people accidentally buying the bundle with the old version they don't need is > just building out your own server-side system, versus a combinatorial explosion of bundles in the App Store that creates a confusing minefield for users.
By jumping through hoops, tying unrelated tools together, confusing users, and reaping an extra $10 you didn't want to take + support costs thereof, yes, it is possible. It is not what we expected or asked for when we started asking for this in 2007 (we = iOS devs).
There are several vendors who do this, for instance 1Password and the Omni Group both do. You have an in-app purchase option that is unlocked by a previous receipt. The challenge is that Apple does not provide tools to help or guidance. They do indeed think e.g. requiring users to buy an upgrade to keep the app working on a new annual iOS version or macOS version is a bad model for users.
Panic even had an upgrade for MAS users when they released their new version of the now defunct Coda outside the MAS (for sandboxing reasons).
Free upgrades are problematic themselves: once you've saturated your market (a good place to be, right?) you no longer have income to provide upgrades.
The first version you sell to a user at full price and offer a discount for upgrading (something like 40% off). It lets the customer pick when they feel the value prop is worth the cost and lets you offer a loyalty incentive to the user.
Right now the choice is "keep paying for it to keep working" or "fully price for every upgrade".