A better JavaScript example would be strict mode, which is opt-in with "use strict" and changes quite a bit of the semantics of the code while being completely interoperable with non-strict JS code.

Yeah, and the "use" statements for this came from Perl which is probably the originator of this pattern here.

Newer versions of JavaScript do not break compatibility with older versions, whereas different editions of Rust break compatibility in various ways while still allowing interoperability between libraries written in different editions. That makes the two approaches very different.