I fail to see any downside to changing this semantics. This has honestly always felt like a language design bug more than anything. Having to write foo := foo a

I fail to see any downside to changing this semantics. This has honestly always felt like a language design bug more than anything. Having to write foo := foo at the beginning of a loop for it to behave as expected is a strong design smell. The gradual breaking (of fix depending on your point of view) with explicit opt-in looks great to me.