I recall seeing something like this before, but the builder had made a sort of floating bridge that spanned the whole length of the blade's path. So nearly all the dust from above was trapped and removed. It was made of clear plastic and the suction hose was hanging down from above the saw so it didn't get in the way. But this would certainly make a difference on crosscuts to workpieces 6 inches or less width. To trap even more, you could extend the plastic channel out another few inches, just above the maximum height of the blade.
The more I do, the less I accomplish.