I don't disagree, but these are in the ~2% convenience at most. With the huge baggage of including C++ in a project. The cost of learning C++ easily outweighs all those benefits. If you happen to have a proficient C++ team (that actually know embedded), go for it!
Speaking more broadly than just the std implementation, but result types like optional shouldn't be a 2% convenience, they should be used in most function calls that return errors. Rust is the obvious example here.
If you argue for Rust I'm all for it, arguably much less of a learning curve than C++ too.