Let's look at planars. Thin sheet of mylar stretched. Magneplanar, Martin-Logan, and other speaker companies using mylar mentioned break-in as early as the 70's with very long break-in periods listed. My extensive experience breaking in such speakers: MG1, MG2, MG3.5, ML Aerius i, ML SL3, ML CLS IIz, ML Vantage backs it up (MG's worse).
As a former builder of subwoofers (ported, non-ported) I can tell anyone that cares that the woofers range of motion increases over time after initial install - sometimes 100 hours, sometimes more before that stops changing. This translates to deeper and more bass. It's a very well known phenomena.
Now if you go listening to a new set of cans for a 100 hours, you may imagine all sorts of things, and experience real things such as: headache, humidity changes, droopy VAC. Then there is the anticipation. I developed a new way for me to do this. Every 10 hours of break-in I listen for an hour - wrapped by an hour on each side of your current reference can. 0-10-20-30 and so forth until you go 3 sessions in a row with no obvious change. HE6SE was my last one, last big change noted at 90, no change at 100, 110, slight change at 120, no change at 130 and 140 - done.
No comment on estats, hedd, ribbons - no experience.
Lots of times the anti-audiophile set is correct. This isn't one of them.