There’s actually quite a lot of software that monetises similarly to what you’re proposing. DxO and Ableton, just off the top of my head. Millions of happy users between those 2.
You get minor version updates for “free” (included in the one-time purchase). Upgrades to the next major version are discounted. Don’t need the features in the next major version? Stick with what you have for however long it works for you.
It’s by far my favourite model because it allows the developers to get paid, whilst not squeezing my neck. Everyone’s happy.