Ideally they will offer a consumer-priced headless system akin to the cube. I could see this in addition to a beautiful all-in-one system like the current iMac.
In order to really get PC users to switch, Apple needs to offer an inexpensive system, that is also expandable. I have many PC friends who say two things. 1) Macs are too expensive for me 2) What do I do with my monitor? If they are looking to buy a low price system they are forced to scrap their monitor and start from scratch. Indeed they would save $200-300 if they could purchase a headless iMac.
I have a 333 MHz iMac at work and it's going on 4 years old. Already the monitor has been replaced (and it's still old and blurry) and the RAM maxed out and it still doesn't run OS X with the programs that I need it to at work. If we could afford to upgrade, we would, it's a non-profit. Granted today's iMacs can hold a lot more RAM and run OS X but perhaps 2-3 years from now people will be saying the same thing about today's iMacs. I think a headless sytem of some sort would mitigate at least some of these issues. If I could upgrade my monitor, I could easily get a couple more years out of this system.