Late in the C++ 20 timeline P1881 Epochs were proposed. Similar to Rust's editions, which at that time had been tried in anger only once (2018 Edition) this proposed that there should be a way for C++ to evolve, forbidding obsolete syntax in newer projects rather than just growing forever like cancer.

Epochs was given the usual WG21 treatment and that's the end of that. Rust shipped 2021 Edition, and 2024 Edition, and I see no reason to think 2027 Edition won't happen.

The current iteration of Bjarne's "Profiles" idea is in a similar ballpark though it got there via a very different route. This time because it will aid safety to outlaw things that are now considered a bad idea. If this goes anywhere its nearest ship vehicle is C++ 29.

Now, Python 2 to Python 3 did take a few years, maybe a decade. But just shipping the mechanism to reform C++ looks likely to take at least nine years. Not the reform, just the mechanism to enable it.