Epycs should be readily overclockable. It's the same silicon as Threadripper. AMD does not, to my knowledge, restrict overclocking in server parts.

Cooling would become a big issue, though. Air cooling a 280W 3970X in a big tower with sufficient airflow to maintain ambient temperature internally is difficult. I cannot maintain max turbo on all cores.

Putting this in 1 or 2 Us in a server would likely be impossible without water cooling (requiring piping to external liquid coolers (whether radiators or chillers)). There's only so much that increasing air velocity can do in cooling.

I don't know if this is the primary thing holding back Epyc specs, but I know it will be an issue.