With feature flags and epochs, it is possible to evolve C++ in the right direction with the minimum of friction and make it opt-in in a consistent fashion. Circle already proves this a feasible approach, and that's a one-man project. There's also clang tooling that modernizes old C++, and huge amounts of work on LSPs and the like for refactoring, so it is possible to provide tooling that mechanically fixes-up a large portion of old code.