For the lower end of the market, the CA1 is the cheapest controller and actually has no subscription cost (from my understanding, its free for CA1 users).
For the higher end, Control4 hardware has fairly competitive pricing imho for the market segment they are in, and the subscription fees are only a small cost.
The Core hardware and CA10 is also fairly powerful (there are some massive jobs using CA10)
Offering hardware refreshes as a subscription wouldn't really work unfortunately. Different users have different requirements. We had jobs for instance with 20 or so controllers, and you'd still need an installer to upgrade the hardware, so it seems more like a service your installer would have to offer. Future updated hardware might not also work with old hardware either (like the old HC-X controllers can't be used in OS3/4, and the Core series needs OS3/4)
That being said, many installers already offer maintenance plans to their customers to allow for software upgrades and basic maintenance.
Composer HE also receives free updates.
From our side of things (Chowmain), on all of our supported platform's we offer free updates too over the life of the driver. There is also no shortage of our drivers from as far back as 2014 (or longer) which are getting some fairly hefty updates too, such as our Generic Lighting driver which had a new OS3.3+ driver added 2 or 3 years ago with completely different capabilities.