I just tried to open the cans and listen to them only holding the drivers and pads like OP says.
And as I thought, and concur with Obify, the sound is vastly improved, with larger sounstage that helps better instrument separation; I would guess they are easier to listen to them for hours now, my main complain along with comfort, since they feel less pungent on the highs, more airy, obviously.
There is no much work to do, just unscrew and drill a hole on the cups.
I would say they sound very similar to my fully open SA5000, with the later having more kick, soundstage and refined sound overall.
I'm wondering if open AT models sound like this.
Does this mod make the M50's leak an incredible amount more?