Yep the 2920x inspired me to only go with 12 cores. What would be even better would be a chip like the 1900X. That chip was like $30 more than a 1700X with more than double the PCIE lanes. Today's $500+ MBs are just porn. I still have my X399 and will be using it as a Virtual hub for some Racing rigs.
Yeah, ideally, starting at 8 cores would be nice. There are a lot of power users who needs lots of IO and memory and good core performance for productive tasks that are not giant batch jobs. (Not to mention it would double as a great gaming rig).
AMD (and Intel) are really screwing up by not satisfying the "HEDT market". Just imagine them selling cherry-picked 8 core ($500), 12 core ($650) and 16 core($800) with slightly higher clocks and higher TDP than mainstream, along with non-gimmicky motherboards at $400-500 (many well featured mainstream motherboards cost this anyways).
If X3D was a gimmick there would be lots of stock.
It mostly affects low resolution gaming and very select edge case workloads, while most heavy workloads see no real benefit if not a disadvantage from heat or throttling. It makes no sense for a workstation CPU.