DDR4 or 5 would really run into bandwidth and value issues.

Bandwidth on that memory interface and setup for dual channel would be significantly worse than Strix Halo, which already exists and could be an entire compute setup with no need for an ASIC.

Consumer grade motherboards generally have 20ish pcie lanes, which more or less boils down to 16x gpu and 4x nvme + something for random peripherals. You'd need something like threadripper to do better.