IIRC theirs are set to 2.5mm at the headphone with 3.5mm as for the device connector. This is pretty common for companies that want to make some form of proprietary connection.

Usually these decisions are media because proprietary connections make them more money selling three or four components of 0.02c cables turned into $5-$25 sales per cable. From a consumer perspective, the only upside to it is that having a replaceable cable can increase longevity, and I suppose from a company perspective in order to ensure 100% compatibility, best to sell your version. That way any 3rd party cables can be the problem.

I think 2.5mm used to be used more commonly on old dumb phones for those headsets and stuff like that. I still see them sometimes but these days it's mostly present on dual plugs like walkies, which is pretty much for mic and audio with a locking mechanism to keep it in place.

Currently I don't have any suggestions for wired/wireless headphones, I wish I did. At the moment my set is the Beyerdynamics DT 990 Pro, I was looking into a version with detachable cables but none that I came across also had wireless - though they're surely out there. It would be nice to have a set to swap between Bluetooth and plugged in.