Even if you stick purely to CPython, it still matters in that there's no guarantee that it'll still be ordered when you update (if you were reading 3.6 dicts). It's not just an implementation detail for CPython, but an implementation detail for specifically CPython 3.6 (and any other version maintaining that status).

So now that its upgraded to language feature, you can actually expect backwards compatibility in future updates.

CPython is not the only Python interpreter out there.