In order for a language to replace C, it has to do two things: 1) be able to write an OS kernel competitive with Linux in this language. 2) get its compiler(s) ported to new architectures, including the Top500 supercomputers, where I work. Note that these two help each other: you make a new architecture, you either code a custom OS in C or port Linux, both of which start with a port of a C compiler. If your language can't do the OS thing, C will remain out of necessity, and be too tempting and stable an alternative.