I would say that's an assumption we as developers need to teach society, but we should really work on teaching it to ourselves first. I can't tell you how many times I've heard "We should just start over" rather than try and understand what we have.
There will be backwards compatibility options for an awfully long time.
A single developer could emulate whatever IO goes to that radio and have it controlled by a simple computer with redundancy. I wonder what they're paying the original developer to maintain this turkey. I imagine he's charging enough to where the sunk cost fallacy is obvious here.
What I find interesting is all the places where FOSS is lacking. There doesn't seem to be a popular and well managed FOSS climate control system. Is anyone making standardized controllers, thermostats, etc? This stuff should be a commodity by now. I'm guessing its hard to work with all the proprietary HVAC stuff and its also an unsexy problem to solve. I'd love to replace my thermostat with a raspberry pi and have a lot of fun modern features. There's a hackaday article about someone doing this, but its a pretty primitive project.
https://github.com/VOLTTRON/volttron from Pacific Northwest National Lab is one example.