I don't think I am. Trading performance for productivity is completely different discussion. It sounded like the claim here was that immutability in the OS (whatever that means) might result in a system with better performance.
We have programming languages where everything is immutable (Haskell). This results in programming techniques that generate a lot of garbage. We have not seen that this results in programs with better performance than those that do not generate garbage to begin with. Why would it be different in an operating system?
Trading performance for productivity is completely different discussion.
The point is that you could possibly buy more for less in this trade off. It's not just GC. It's a close to pauseless incremental GC that might become available.
It's not so much that it has to be in an OS, though it seems it would be better in an OS, however.
We have programming languages where everything is immutable (Haskell). This results in programming techniques that generate a lot of garbage. We have not seen that this results in programs with better performance than those that do not generate garbage to begin with. Why would it be different in an operating system?