C++

Whatever reasons anyone advances for it, the Clang project's choice was, manifestly, C++. If you don't understand the choice, it tells us more about your state of knowledge than about the language.

People actually building things that have to work well aren't much concerned about how "pure" a language is: they want to use whatever best helps them get their work done, with a minimum of fuss, bother, and risk. Among the alternatives available, it's not hard to choose. No successor to C++ is anywhere on the horizon, except for C++09 itself.

A language equally as powerful as C++, but much simpler, is certainly possible in principle. Part of the reason no seriously considerable replacement for C++ is in the works anywhere is that academia is the only remaining milieu capable of nurturing a new language, but academic computer scientists are, as a rule, actively hostile to concerns of industrial programmers. Working on a plausible successor would be death to one's academic career.