You're right about ECC support on consumer Ryzen motherboards, it's done on a best effort basis by the motherboard manufacturer even thought all Ryzen CPUs technically support it, and YMMV. However this is made by ASRock Rack, their enterprise/workstation grade server brand. Although the X470D4U and X470D4U2-2T both use Ryzen X470 "consumer" chipsets, they have been explicitly designed and validated with ECC memory in mind. It's not mandatory, and non-ECC memory is not incompatible as @Ookgluk32 suggested in their original post.
I have several deployed systems built on this platform with ECC memory from ASRock Rack's QVL and it works perfectly, and I haven't seen any of the symptoms or issues in HardwareCanucks' thorough article in my testing.
As this is the first in (hopefully) a long line of future Ryzen-based server motherboards, can PCPartPicker please review their policy on ECC support and memory compatibility for server components?