I think the main point is that shaving the iMac below 2011 thickness is pure form-over-function wankery. Even if they are set on sacrificing perfomance at the altar of volume reduction, weight reduction or whatever, they should do it by removing the "lip" rather than thickness. That would have ergonomic benefits in addition to making the machine look better from the direction the user is actually looking at it from. And they should restore VESA compatibility to all models, especially if they can't or don't want to deliver a decent display foot to begin with.
Having more volume and weight allowance for cooling always helps. It's not necessarily just a matter of increasing performance. For instance, a midrange desktop GPU would deliver the same or more as 780M but cost a lot less since it can be a smaller chip, higher clocked, not so highly binned. Higher margin for Apple and/or lower pricepoint for the customer.
Naturally I agree that an xMac would make more sense for any kind of performance. Such a machine existing would let also Apple seriously pursue the design-object mentality on the iMac, go 100% integrated graphics, perhaps 100% passive cooling, to deliver a truly breathtaking machine in that vein instead of these silly compromises.
I agree to a point on the new iMacs. Doing things like fusing the display to the glass have tangible benefits beyond saving space (complaints about self-repair aside.) I was amazed to learn they were still using 3.5" drives before that revision. And I definitely think they could have made it thinner than the 2011 without going to the 5mm thickness and forcing some of the concessions they did, like the non-upgradeable RAM. The chin is curious—it's obviously gotten smaller but at this point I'm not sure what the point of it is, besides maybe needed more space than stacking the display on top would provide for cooling? There's nothing but vents down there now. I think there's an argument to be made for aesthetics, but you could still dramatically shrink it down by almost two inches or so and still have room for that strip of aluminum and an Apple logo.
As for the xMac… I dunno, I feel like with the new Mac Pro, and the continued presence of the Mac mini, that ship has truly sailed (and I mean it was always a dream, wasn't it? I don't think there was ever any indication from within Apple something like that was coming.) Since the demise of the G4 there hasn't been a midrange utility Mac that is more customizable than an iMac or starts off very cheaply. (I remember those $1400 price points for the G4 Digital Audios…
In a sense the Mac Pro does meet some of those goals in being a small and quiet base unit, but of course its designed for external expansion and dual GPUs which non-pro users really don't need, and at least at this point there's no indication that they'll ever be ways to customize it more to your specs (like taking out a GPU and putting another SSD there or summat'.)
Personally my dream new computer would have been something between the old and new Mac Pros—just something with at least a slot for another SSD inside, and maybe 6 RAM slots instead of four. (I'm holding out hope for another SSD in a later revision, personally; it seems the only reason there isn't another one mounted on the second GPU like on the first one is that there just aren't any more PCI lanes to use on the thing once you've gotten the GPUs and the Thunderbolt busses, as opposed to heat or noise constraints.)
Speaking of which, someone was talking about whether or not Apple would make the Mac mini smaller, and I honestly hope they don't. It's a great little computer with the two drive bays. I'd love for them to offer some of the MBP's features like the Iris Pro graphics, too--the past couple of revs the Mini has sort of tracked along with the 13" MBP rather than the 15", in terms of graphics capability.
EDIT: One thing though, isn't VESA compatibility still a thing? The only caveat being you have to specially order it and you can't use it with a regular foot, it[s VESA only at that point.
http://support.apple.com/kb/HT5619
