The loss of the hard drive bays really doesn't worry me (is anyone doing serious work really not working off a big RAID or a SAN?), and my audio interfaces have

The loss of the hard drive bays really doesn't worry me (is anyone doing serious work really not working off a big RAID or a SAN?), and my audio interfaces have been external for years... The only thing I might want is a PCI-Express slot for a RED ROCKET card (it's a hardware decoder for 4K+ video from RED cameras) but I've never really felt the urge to splurge for one of those - both Final Cut Pro X and Premiere Pro are good enough at decoding it with the CPU and GPU even on my MacBook Pro so the Mac Pro should have no problems with it... The only time I feel it is rendering (you can work in 1/4 res [a bit more than 1080p] but for finishing you want full quality even if you're downscaling). And if I did want one, there are a number of adaptors that work with them...