I don't think performance costs are that big of a deal in general. The real costs with those sorts of services is perhaps centralization and dependency on an outside entity.

If we did manage to create some magical cross-language library (compile everything to C?) then maybe libraries would be back in style.

I don't know, at least on the JVM, libraries are very much in style. I know Google writes most large internal libraries in C++ with a C API and uses them from Java, Python, Go and C++.