IIRC there has been discussion about VCA's in the past, which basically boiled down to the idea they are not needed and because similar can already be achieved by other (
not so convenient) means. I have a feeling though that if they were introduced they would be welcomed by those who argued against there usefulness or need, IMHO it's just that SONAR doesn't have them and other DAW's do, so it gets put down out of hand, which of course would have been different had SONAR actually had them, but that's just me.