What distinction are you drawing? I think concerns like "this operation is O(n^2) in the length of the passed list" are absolutely the responsibility of the language, and probably even lower-level details. I'm not sure how to expose "this operation takes n machine-code instructions" without sacrificing cross-platformness, but I do think that's something we're going to need for important use cases (e.g. cryptographic libraries need to be able to do various things in constant time, which no existing language really has first-class support for).