A laptop in clamshell mode is a good substitute for a headless mid-range machine. Combine it with a BookArc stand to avoid wasting desk space and it's hard to beat.
In many respects, the new Mac Pro is exactly the all-round machine (development, scientific computing, plus the odd game) I've been waiting for. If it shows up with a reasonable low-end version, I'd buy it in a flash (or even sooner, given an Nvidia GPU option). But Apple have been very wary about releasing mid-range machines which might cannibalise iMac sales, so I'm not holding my breath.
Maybe most professional audio guys don't actually require a serious workstation anymore; I'm sure Apple is calculating or hoping that it will be good enough for enough video editors too. It's hard to see the 2013 Mac Pro getting under the desks at Pixar, but presumably Apple feels willing to give up on that end of the market.
I've wondered: if computer makers sold laptops with lights-out-management and detachable displays, would people would repurpose them into makeshift mobile servers and design entire server farms around them, like they have with the Mac Mini. You could have a work/coding environment where if somebody needs to take home the dev server to hack on it overnight, they pull it out of the rack, slap on a display, use it any other laptop, and bring it back in the morning to plug back in.