Please don't confuse this with an issue of what I want. It's just what I think the name implies.

"Backwards compatible" implies, to me, that if I take out the new features from the language, I'm left with legal code in the original language. This is markedly different than being able to call one language from another. I can call Fortran code from C, and I would never characterize Fortran and C as "backwards compatible."

One is about source code compatibility. The other is about object code compatibility.