OK, so a few things about this that I'm seeing...
3200x2000 background: A bit odd choice of resolution, but I think they're making a 16:10 resolution that they'll crop to 16:9 for the machine with an actually 3200px wide display.
But, that does indicate a few things.
3200x1800 makes sense if you're pixel quadrupling a 1600x900 display, which is what a 15.6" 16:9 MBP at current pixel densities would be. But, it DOESN'T make sense for pixel quadrupling the 17" MBP, or any of the desktop displays.
If the 15.6" or 15.4" MBP gets this, and the 17" doesn't... that means that (and this is pure conjecture here) the 17" isn't long for the world. How well do they sell, anyway?
As for display technology supporting a pixel-quadrupled iMac, we've had the technology for a pixel-quadrupled 21.5" iMac since 2001. The IBM T221, a 3840x2400 22.2" monitor, is the same density as that theoretical display. It was $18,000 when it came out, and by the time IBM pulled the plug on IDTech, a Viewsonic-branded version of the T221, the VP2290b, was in the $4000 ballpark in 2005. So, had the T221 followed a curve influenced more by technology improvements than by the market getting saturated with unusable monitors, we'd be seeing these panels in the $2000 range nowadays, as a standalone monitor, I think.
Now, to look at all the machines that Apple has. Keep in mind that I think that only pro hardware will get this, and Apple likes to stick to around 100-110 PPI for desktops, and 110-130 PPI for laptops.
I'll go ahead and speculate on theoretical 16:9 variants of existing models, too.
MacBook Air 11.6": Currently 1366x768, 135 ppi, retina at 25.4" - would be 2732x1536, 270 ppi, retina at 12.7"
MacBook Air 13.3": Currently 1440x900, 128 ppi, retina at 26.9" - would be 2880x1800, 255 ppi, retina at 13.5"
MacBook and MacBook Pro 13.3": Currently 1280x800, 113 ppi, retina at 30.3" - would be 2560x1600, 227 ppi, retina at 15.1"
MacBook Pro 15.4" low-res: Currently 1440x900, 110 ppi, retina at 31.2" - would be 2880x1800, 221 ppi, retina at 15.6"
MacBook Pro 15.4" high-res: Currently 1680x1050, 129 ppi, retina at 26.7" - would be 3360x2100, 257 ppi, retina at 13.4"
MacBook Pro 17.0": Currently 1920x1200, 133 ppi, retina at 25.8" - would be 3840x2400, 266 ppi, retina at 12.9"
iMac 21.5": Currently 1920x1080, 102 ppi, retina at 33.6" - would be 3840x2160, 205 ppi, retina at 16.8"
iMac/Cinema Display 27": Currently 2560x1440, 109 ppi, retina at 31.6" - would be 5120x2880, 218 ppi, retina at 15.8"
Theoretical 13.3" 16:9 low-res: 1366x768, 118 ppi, retina at 29.2" - would be 2732x1536, 236 ppi, retina at 14.6"
Theoretical 13.3" 16:9 high-res: 1600x900, 138 ppi, retina at 24.9" - would be 3200x1800, 276 ppi, retina at 12.4"
Theoretical 15.6" 16:9: 1600x900, 118 ppi, retina at 29.2" - would be 3200x1800, 235 ppi, retina at 14.6"
Theoretical 17.1" 16:9: 1920x1080, 129 ppi, retina at 26.7" - would be 3840x2160, 258 ppi, retina at 13.3"
Hrm. I am noticing a problem here for getting consistent resolutions when getting 16:9 into the mix... and, interestingly, Apple stayed on 16:10 for the 13.3" MBA. So, I wonder if this could even be a red herring of some kind? Because 3200x2000 doesn't really match up with any expected 16:10 resolution...
(Current lineup can do 255-270 ppi, which is fairly tight, ignoring the 13.3" MB(P) and the low-res 15.4" MBP, but going to 16:9, either desktop area would shrink for many users (and even then, the 11.6" and 17.1" wouldn't fit in well), or there would be a wide variance in ppi.)
Another thing to consider is the $3.9 billion that Apple pumped into LCD makers... possibly to secure a supply of retina panels?
(In case you can't tell, I'm SERIOUS about my high ppi displays. Looking at a IDTech IAQX10N, a 2048x1536 15.0" 171 ppi IPS display right now, and I'm stuck on a 5 year old machine because of it. Whoever makes something roughly equivalent or better gets my business, unless they're Sony.)