Isn't C++ already a serious contender to C? It clearly has not replaced C everywhere, but it's taken over much of C's market. And if C++ could do it, I don't see why another language couldn't do the same (that's not to say that the next language to do that already exists today).

One thing that's important to notice, I think, is that low-level languages' combined market share has fallen sharply since the 1970s, and it doesn't seem that the trend is about to sharply reverse direction. To me that suggests that if a low-level language wants to be more popular than C++, it should focus on low-level programming and shouldn't try to also be a good applications programming language (as C++ has tried to do that, but the overall market share of C and C++ is lower now than it was in, say, 1990), but I could be wrong about that.