But the problem with sliding doors is that they have to slide somewhere - so to maintain the smooth continuity of the boards, they'd have to shift in or out to open (probably in because out causes more problems with boardline continuity when the doors are open). I suppose you could have the door drop down into a cavity below the boards without shifting in or out - not sure if there would be a concern with icemaking equipment or pipes down there. This would have to be a robust system that could handle players stepping on it - and there'd have to be some safety mechanisms so the door doesn't fly up and nutpunch a guy getting off the ice (or suddenly drop down when someone's leaning on it in a board battle). Also limbs/fingers getting caught, etc. And if you've got sensors to prevent that, they could get screwed up and then the door is permanently down. Probably all too much trouble to be worth the benefit of these rare injuries.