If the C6H gets it, it'll be unofficial, derived from ASUS' own work on the C7H (which is essentially the same board as the C6H), and naturally X370 would be the last chipset that could get support, as the 500 series and 400 series are in line. We're last.No one can affirm or deny that the C6H will have the ryzen 4000
As we've always told people here, wait and see. There's no further answer, really. Wait and see.
If there's no Zen3 support, you could always drop in a cheap 3900x/3950x from people who will be upgrading and still have a great workstation, or you can upgrade the motherboard to a 500 series board and get a Zen3 CPU. Your choice.