Exactly. Change it to 17GB per layer, and no current drive will be able to read it or write it. Make the drive an HD DVD only drive (give up the essentially useless DVD movie playback), and you have a system which is secure even if you compromise the drive firmware, which is basically the only part of the 360 which has been compromised (except for one quickly fixed hypervisor bug, introduced, amusingly enough, on the HD DVD addon update disc)
If you can say, do you know what an HD-DVD drive maxed out at in terms of read speed at an appropriate accoustic level?
P.S. The firmware updates have been pretty funny, one of my friends has given up on the idea of a chipped Xbox 360 because of the number of times it just stopped working, 2-3 times so far IIRC. Just now I believe there was a compulsary update in the Assassins Creed: Brotherhood DVD and it completely nuked his 360 and all the game saves are coming up as corrupted when he tried his HDD on my 360. I kept telling him it wasn't worth the hassle, he kept not listening to me and now hes upset that his collect of 100+ games is useless. Guess you won back a paying customer and sold a slim Xbox 360!
P.P.S. Is there any indication of whether we're going to be able to sync our WP7 phones to Xbox 360? We Xbox + WP7 customers need to be beloved by EDD since we're buying more of the products than anyone else!