Never read "smallcultfollowing" before.

The "implicitly copyable" problem is amusing. That was dealt with by Wirth in Modula 1 with the rule "if the programmer can't tell, it's up to the compiler". Thus, non-writable objects could be passed either by reference or by copy, depending on object size. This was up to the compiler. The usual rule was that anything up to 2 words in size was copied. Since the called function couldn't change the value, it didn't matter.

This avoids philosophical gyrations. You want a rule that says you can copy ints and floats, for performance reasons. Trying to reach that via type theory makes it harder. It's an optimization.