So what will happen if you place a 32-core / 64-threaded AMD Epyc processor onto an ASUS X399 Zenith Extreme? Would it work, would it even boot or pass the BIOS POST stage? Well, somebody has tried that and posted a video on it. The result, suffice to say are only mildly satisfactory.

It was Der8auer who tried the Epyc processor onto socket SP3 / Threadripper on socket TR4. To get this processor working. In order to get the processor working, he bypasses what is called an ID pin, once that pin does not make any contact with the motherboard you create a bypass that allows the processor to boot, he actually accomplished that by placing some insulation taped over the ID-pin (see photos).

After power on the debugging LEDs become active, and it all pretty much ends there, as the BIOS procedure stops posting at the memory check. In theory, EPYC should be able to work on X399 as the platform is the same. However, and obviously, you're going to need a properly EPYC supporting BIOS. 

I have a feeling that this story hasn't ended just yet ..

Tweaker gets 32-core AMD Epyc-CPU partly working on ASUS X399 Threadripper mobo