As others has stated Apple's competitors have systems that spec out and price out exactly the same. And the exterior design has now pretty much become "iconic"
by definition creative people create... ever moving forward, to stand still is to cease to be creative and become stagnant and gather cobwebs, Icons are highlights in the timeline of our growing past.
Now we are discussing the state of present /future and change, and the present Icon Macpro has outlived its shape and form but not yet its use,
Marvin speculates future development quite well but it is always dangerous to look too far down the line into too many possibilities, and as creative people we need to grow to the next stage in the here and now frame.
Macbkpros and iMacs are set to become the user thin client interface devices and I would use them in any studio setup but not on a recording desk, not on a pro video edit suite, and not on a stage control video server setup.
ask any engineer if he would prefer lugging around a 40 minis rack instead???
Every accessory comes on PCIe cards and the next development from Intel builds on that specification, its easy to imagine the next Macpro undergoing a new radical design iteration to accommodate these new technological advances,
If I were to design a new studio today I'd want a micro cloud system connected live to the macro cloud dissemination of the web. therefor optimizing a new macpro design to have multiple user configured preferences albeit either a studio desk system or central local server and on even to thunderbolt mutinode internet service provision.
"Time waits for no man" and mechanical drives and the disc have had their time solid state memory cores are here the future has arrived and Intel are adopting PCIe card SSDs as their next standard hence my ideal future macpro being reduced in size but still a studio rack mountable duel Zeon processor M/C having 8 full size PCIe card slots and optical thunderbolt stackable, what more could one want?
In my experience I've inevitably found the simplest neatest solution to be the right one.
and what is to come 10 years hence will have plenty of time for new discussion I'm sure.
This of course does not detract from the 27" top of the range iMacs ability to be a wonderful stand alone client device that equally has many niche uses aswell which can also connect to a businesses micro cloud Macpro based server system the software of which is now included in Lion OS.
or indeed the mini that has many domestic uses ahead of it, but I don't think any studio engineer would want a rack of 40 of them gracing his room in place of a Macpro.