Tight integration with the language may be beneficial in making it simpler to write, but its not like you can't do this already in other languages. Baking it into the language might be useful to make it more popular. Nobody should be doing the chain rule by hand in the 21st century.
You can use CasADI to do automatic differentiation in C++, Python and Matlab today:
https://web.casadi.org/
Tight integration with the language may be beneficial in making it simpler to write, but its not like you can't do this already in other languages. Baking it into the language might be useful to make it more popular. Nobody should be doing the chain rule by hand in the 21st century.