This is a very unwise and shortsighted take. Not deprecating features right away means everyone's life is made easier as you can upgrade manage full/partial project upgrades to newer C++ standards without having to resort to tickets blocking your critical path with all-or-nothing upgrades.
And this does not stop at your projects. Dependencies are also covered. Do you believe it's in your best interests that you lose your ability to up point releases to your
Lastly, why does it bother you that backwards compatibility is a Hallmark of C++, and deprecation is a multi-standard process? You're free to stick to a subset if that's what you want. What's the point of getting all bothered with being able to continue using features without seeing them break under your nose for no reason other than a version bump?