Will the new ACD replace existing ACDs?

I'd regard it as an additional product. If you look at the pages on Apple's site for the ACDs and compare it to the one for this there are huge differences in how they are being marketed. Whether Apple will continue to offer "pro" displays remains to be seen. I would expect it to become evident in January and we will probably see a 30" then too. They may do away with 20".

 

i'm also wondering if the 24" replaces the 23". as umbongo says they are being marketing in a very different way but it may still be the case that the 23" will quietly slip away when the 24" is available in november.