I think you missed the main point, which was the "billions of lines of code" part.
It's not a question of simply retiring C++.. it has to be replaced with something. Even safe languages frequently rely on libraries implemented in C or C++ as part of their runtime.
Even if you were willing to pay a 100% performance penalty (and there are plenty of places where I'd be fine with that), it's still a massive undertaking.
And usage of C++ is still growing exponentially, so the number of lines of code is growing faster than our ability to rewrite/replace them. I know, it's a losing battle. We'll never do it. We are stuck with C++ until the end of time because of the sunk cost fallacy. If everyone who currently works on C++ instead switching to rewriting instead of adding, we'd be able to replace everything in 5 years.
If C++ is only kept around because of a few libraries needed to implement the runtime of safe languages, then I would consider that some kind of victory.
It's not a question of simply retiring C++.. it has to be replaced with something. Even safe languages frequently rely on libraries implemented in C or C++ as part of their runtime.
Even if you were willing to pay a 100% performance penalty (and there are plenty of places where I'd be fine with that), it's still a massive undertaking.