It's quite a leap from "certain observable behaviors of the runtime" cannot change to Go is a dead-end.

Go regularly makes runtime changes and language changes, see https://go.dev/blog/. Some highlights:

- Iterators, i.e., range-over-function

- Generics

- For loops: fixed variable capture

- Optimized execution tracing

- Changing the ABI from stack-based to register-based.