I wouldn't want it.
As someone said, I haven't had a single crash where I would have wanted my board to release. I'm sure you can come up with some scenarios, but those would definitely be very abnormal situations. I've watched skiers having so much fun trying to get back to their gear after they slide down the hill and it stopped
Plus, if you had it on a leash with an intense enough crash, it suddenly turns into a projectile that's going to come back and hit YOU. No thanks personally.
(Don't take this personally. It's definitely an interesting idea, but I don't see a need to change what we have now. If you really hate strapping in after the lift, just grab some flows or something)