I think this is my first ever post in this community so excuse me if my tone or message is inappropriate or not in-depth enough.
I have to say that I read this proposal and I immediately thought 'why isn't this happening already?' Meaning, I'm a huge fan of all the low-level stuff Apple has been doing over the years, like LLVM and the continuous improvements the Compiler team does to keep our code as fast and lean as possible. And given how crazy Apple is about maximum performance and efficiency, I would've thought that Swift being in version 5.1 already, this would be a thing, though I understand why it isn't.
As such, huge +1 on my end. My only question would be how does this complicate future development of getters and setters, since by my experience, making things 'smarter' often makes thing harder to work with down the line.