I heard the $4000 Focal Utopia Headphones yesterday


Very nice. Very expensive. Beryllium drivers.  Reviews a bit hyped I think. Who would pay that premium otherwise? Not sure I could live just with any headphones still.

mapman
Don't know if they are worth a try at $4000 but I have a pair of Shure SE846 IEM for $1500 and I have never heard anything even remotely as good in an IEM.  These IEM sound very close to the very best open back cans I have heard and have incredible noise reduction because of the great seal with memory foam.
Beryllium dust is deadly but as no one will be subject to beryllium dust from a set of headphones I think you are good. I don't suggest that anyone should extract the beryllium diaphragm, drill it to create a cloud of dust and then inhale deeply :) other than that you are safe.
For far less yhe Stax Electrostatic head phones are magical 
There are many sub $1500 headphones that are exceptional. $4k for headphones is a rip off IMO.