While Herb uses modest language when describing his project, my take is that's because it's a huge effort that might fail, but it does not indicate lack of ambition. If anything, I think this is hugely ambitious. The work in the standards committee provides the necessary infrastructure to make this feasible in the first place. On his Github he lists the changes that went into C++ over the last years that enable this prototype.

It's pretty clever really, and dare I say, it seems feasible. This essentially creates syntax bubbles inside the language where there are different defaults, and then transpiles those bubbles to regular C++ while copying the rest verbatim. See this https://godbolt.org/z/nPPMYM3Yj as an example how array accesses are transpiled to do bounds checking.