I don't think there has really every been a headphone that was just purely engineered for slam... Has there? Except the xb series, I can't think of anything made directly for the extreme basshead niche... It would be lovely to have a company work directly with Hawaiibadboy to create something though. Probably be some ridiculously powerful driver... Like the equivalent of the 1.5 Tesla on the AKG k812... And probably would be like 70mm for a subwoofer and 40mm for the middle and treble.
There is a "safe listening level" barrier. It's a legal one and it's strict in the E.U. I believe?
I think the safe listening threshold has already been reached. If they built an efficient 70mm sub and 40mm driver it would be able to damage your ears too easily. Buncha kids with no hearing....maybe the Chinese make one as a proxy attack on our youth and America's future by making us all deaf