If I could plot a graph of xMac likelihood, I reckon it would be peaking right about now, albeit at around 25%. Between intel's roadmap, the recession, and the conflicting rumours about the mac mini getting bigger/smaller with less/more features and power, the promised land cannot be far away.
The fact is that something drastic has to happen to apple's desktops now anyways, purely because of the way nehalem is being rolled out. Whether it be desktop-class chips in the iMac (surely a tall order now that they're half the thickness of the g5 days...?), Mac Pro (which seems like a big step down), a bigger mini or (gasp) a new product altogether (that looks suspiciously like the cube), there is no way apple can twiddle their thumbs waiting for mobile variants whilst dell gets a 6-month lead on this generation of processors.
Come fervent product-line-gap-denying zealots, fanbois, protesters of cannibalism and even the few rational observers of apple's nichey marketing strategy (by which I mean you, Tallest Skil): heap your venom upon us. For my own part, i'm used to it. I may relent and buy an MBP with external display but I will never give up hope. Why, just 2 years ago most of this forum was adamant that there would never be a multitouch fullscreen video ipod, because it would cannibablise iPhone sales, even tho the iPhone hadn't even come out yet and the iPod had an 85% marketshare to protect.