[luddy]

>> Go has built-in mutable containers, and no const, yet they still use SSA.

Right, as you say, compilers are converging on SSA, and almost all languages have mutable containers. All it means is that there's a mismatch between the semantics of the IL and the semantics of the language. That's a fairly common situation; there are lots of semantics (like concurrency and associated memory consistency) that can't be captured in an IL as they occur in reality, in the language being compiled. It's just a thing that has to be worked around.