This is a great opportunity for people who actually have those cards to test and report the results. It shouldn't be hard to switch it on and off for different parts, people just need to report whether or not it works for them.
Originally Posted by Adarion
If there aren't enough people out there to do that, then there's a very strong argument to be made that it's not important enough to waste anyone's time from AMD on it anyway.
If someone is interested in contribute testing there is still Hyper-z to test and enable on R300/R400, see http://www.x.org/wiki/RadeonFeature/ .