I'm not a fan of those mITX designs where the Socket is almost as big as the Motherboard itself. AsRock already has experience doing things like that since the days of the
X99E-ITX/ac, but I think that it is stupid and wasteful to design for platforms intended to have plenty of expansion options then force them on small form factors where you have to cut DIMM Slots, PCIe Slots, etc. Sure, there are people that may think that the compute density could be great, but I'm not one of those. They are limited.
Going back to the EPYC3451D4U-2T2O8R, that thing is almost my dream EPYC Embedded Motherboard. Just look at ALL it has:
An ASpeed AST2500 BMC for IPMI and remote management. I'm still waiting to see the newer AST2600, which supports DisplayPort out of the box so it can get rid of old VGA Port
An Intel X710-AT2 NIC (The new Intel NIC I made a Thread about half a year ago) for two standard 10G Ethernet Ports
An Inphi CS4227, which is a PHY, not a full NIC. THIS MEANS THAT THIS MOTHERBOARD IS ACTUALLY USING THE AMD EMBEDDED 10G MACS!!!
6 OCuLink Ports. 4 are pure PCIe, the other 2 are PCIe or 4x SATA each. I don't know if there are any disadvantages of OCuLink, it seems to serve the purpose of a smaller U.2 and the cables are cheaper, too. Note that most of the OCuLink Ports seems to be shared with something else, so its one thing or the other.
mATX with 4 Slots, so you have plenty of expansion. There are 2 PCIe 16x Slots, but only one works at full 16x at all times. The other works either at 16x or 8x if also using the integrated LSI SAS3008 SAS Controller.
I love it, is a solid take on mATX. Sadly, I'm not a fan of the dual die EPYC Embedded models due to the NUMA Nodes, and they're technically already 3 years old. If a product like that was available at launch day and could be directly compared to first generation ThreadRippers it would have looking much better, now I'm just waiting to see when AMD is going to update the embedded lineup.
Also, price will be absurd. Should be no less than 1500 U$D judging by just how much the EPYC Embedded 3451, the BMC, the NIC and the SAS Controller seem to cost.