Most of what I want to look at is above 60 foot depth. The prettiest coral and fish are usually 30 to 40 feet, so a discharge hose to the surface should be possible, as long as you're aren't moving too fast. But then that's the idea of a sled, isn't it? Maybe just a hose that trails behind. If the source of the noise is ten or fifteen yards behind, you probably won't disturb the critters much until you're already past them. If it gets hung up it could pull off easily. You'd know it immediately and could free and re-attach it.

I dive like I wheel the Jeep - in a super-slow mode. I cover less distance, but burn air a whole lot slower and probably see more than the average diver. On the few group dives I've done I'm often about ready to turn around when the rest of the bunch is getting back on the boat, so I don't see the need for a powered sled except for a few specific purposes. There have been times when faced with a long snorkle to reach the dive spot that it would have been nice, but then what to do with it during the dive?