Apple's business strategy is to build machines for specific markets and make a profit, not jump into the bottom-scraping morass of building cheapo boxes just because a couple thousand geeks are crying for one.
What bugs me in this thread is that most detractors assume that another headless Mac absolutly means "bottom-scraping morass of building cheapo boxes".
Desktop components are not scrap or junk, they are just cheaper than mobile parts. That makes building a computer with desktop parts less expensive than an equivalent one with mobile parts.
mobile DC 2.40GHz cpu =$241 / desktop DC 2.40GHz cpu = $113
mobile DC 2.50GHz cpu =$316 / desktop DC 2.53GHz cpu = $133
mobile DC 2.60GHz cpu =$530 / desktop DC 2.66GHz cpu = $163
mobile DC 2.80GHz cpu =$851 / desktop DC 2.83GHz cpu = $163 (same as above)
mobile QC 2.53GHz cpu = $1,038 / desktop QC 2.50GHz cpu = $266
Desktop chipsets are not worse than mobile chipsets.
The size isn't even a problem anymore, Intel has/will have G45-based mini-ITX motherboards (6.75"x6.75") just a little bigger than the Mac mini.
If Apple wanted to, they could build a desktop Mac mini a tad bigger using desktop components that would cost less to manufacture and, if priced the same as the current Mac mini, would generate more margins. It would not be a cheapo/junk Mac.
At one time, people could say that Apple was doing economy of scale in build most of its computers based on the same platform, but it is not the case anymore. Each line has it's own chipset and cpus:
Mac mini: Napa chipset (GM945) and 1.83/2.00GHz 667FSB C2D cpus
MacBook: Santa Rosa chipset (GM965) and 2.10/2.40 800FSB Penryn cpus
MacBook Pro: Santa Rosa chipset (PM965) and 2.40/2.50/2.60 800FSB Penryn cpus
iMac: Custom chipset (Montevina-like) and 2.40/2.66/2.80/3.06 1066FSB custom penryn cpus
I really don't see why another desktop Mac (replacing or not the Mac mini) couldn't have "quality and design" because it uses less expensive desktop parts or couldn't generate the same kind of margins.