> which doesn't take backwards compatibility very seriously

I go out of my way to make sure fish still compiles on ancient versions of operating systems (with the most recent compiler you can get on them) and still remains functional in the kernel console (no X), and others on the team go to even further extremes. We’ve argued for weeks over changing the names of variables that might break older fish scripts, even though fish isn’t really a non-interactive scripting language.

You’re going to have to qualify that statement.