Maybe now is a good time for Apple to introduce a headless iMac with more expandability than the Mac Mini but less expensive than a Mac Pro.
In this economy I don't want to buy a computer with a monitor grafted onto it, my existing monitor works just fine. I need more power what the Mac Mini offers and I can't afford a Mac Pro. A desktop-class video card would be nice too, not the mobile video cards Apple sells in everything except the Mac Pro (IIRC).
In other words, a scaled-down less expensive Mac Pro with the same power as an iMac, please.
It is unlikely that Apple will do this any time soon. They are still selling plenty of iMacs and Mac Minis, and as a relatively marginalized segment of their revenue stream, desktop computers don't exactly command the attention of Apple's execs and engineering teams.
As always when you analyze a company's future direction, you have to look toward profits and internal development/investment. The economic utility of producing a headless Mac will be relatively low because of the [1] opportunity cost of diverting internal resources to its development, [2] its relatively low margins, [3] its likely cannibalization of more lucrative existing desktop devices, and [4] the fact that the desktop division as a whole is pretty small-volume and low-impact to Apple's bottom line.
Right now, I am of the opinion that iMacs are a pretty terrible value proposition. They are less powerful than / roughly the same powerful as the quad-core Mac Minis, and you can easily get two or more high quality 27" QHD displays with the difference. They key differentiator is the graphics card. I think people underestimate at times the CPU capabilities of the Mac Mini. If you don't game hardcore, it should be more than capable (and far more so than the entry-level iMacs).
Here's another problem with a headless Mac. People will want to upgrade it. A lot. And Apple does NOT want to support people's desired hardware configurations. For instance, they won't write kexts to support graphics cards they don't use. They will not want to become a driver support center like Microsoft has to be. Unfortunately, your best bet would be to build a Hackintosh. It's really easier than installing Windows these days. I too would probably love to have a headless iMac, but it honestly just won't happen if Apple continues to be the Apple we know. However, there is hope. Thunderbolt has been pretty disappointing, but if useful TB graphics card chassis become a reality, you could have your PCI-e graphics with a Mac Mini. Still not ideal, but it's a start.
This is really Apple being Apple. If you've been a long-time Mac user (and I mean PPC and earlier), you know that if you need something Apple doesn't offer, you're going to have to make do on your own. Apple doesn't give a **** about your desires and never will unless it is conducive to their bottom line. Yet we all keep buying...