Running C++ in a browser app? Can't see that one blowing up in anyone's face.
Of course, the big probale is you need a language that can be made to run in a very secure sandbox. Java, python, and related languages could be made to do so with some work. They run on VM's or have an interpreter. But C++? If you're talking about creating a new implementation that runs in an interpreted/virtualized/sandboxed environment and has built-in memory management thrown in, then that might be a possibility. But then again, why would you want to do that when there are so many other ones out there.
Real Users find the one combination of bizarre input values that shuts down the system for days.