Re: "shifted their focus to proving the opposite –..data races under specific circumstances."
But how many people use "Erlang, Rust, Go, Scala." ?
And which ones will still have a developer pool you can actually recruit from in a decade?
Erlang has been around for nearly 30 years, Go for about ten. How much track record do you want? FORTRAN?
As for your second point, it essentially equates to asking how many developers are left after you deduct web monkeys and Java/C#. The answer to that will always be "not many", irrespective of the specialism in question. How easy is it to recruit a FORTRAN expert?