Pairing with multiple devices, auto shut off feature, lighter and better noise cancelling. Looks like a good enough upgrade to me. Also that silver looks a tad bit more silver than the previous orthopedic shoe color. 
Compared to my previous XM3's, the XM4's feel a bit lighter and the finish feels more matte.
These headphones primarily reside at my workstation, so connecting this to both my phone and mac mini is godlike!
Once I turn on the headphones, they connect instantly to the first device. The second device however takes a few more seconds to connect. I do like that the voice assistant tells you that the "2nd device is connected" despite how long it takes to happen.
I'm definitely not going to use the Speak to Chat feature since I find myself rocking out singing with the music I'm listening to at times. Having it pause in the middle of my concert is super lamesauce!
All in all, I'm extremely satisfied with these cans regardless of the minimal quality of life features. It's still good enough for me to upgrade and also if it ain't broke, don't fix it. 
