Hackable Mac
What I think Apple should do is cater to the modders out there and make a Mini that can be easily upgraded and customized by the end-user.
The Mini - which hasn't been upgraded by Apple in a long time - is allowing end users to try stuff like adding the Core 2 Duo processor, RAM, hard drive, etc. on their own.
This kind of behavior has been happening on Windows machines for ages.
The Mini was supposed to be the computer that brought people over from the PC side by allowing them to use their own keyboard, mouse, and monitor. Heck, now show them they can upgrade the processor, hard drive, use a different optical drive, skin or paint the case, dual boot into Windows, etc and you'll win over other converts.
The iMac and the laptops are more closed systems. And the Mac Pro isn't a consumer model that will be modded by the average user.
If Apple drops the Mini in the hopes that the Apple TV will fit the bill, I think they would be making a huge mistake and giving up on the person who might want to play around and soup up a Mac to see what they can do. Or introduce a Windows user into Leopard.