To some extent it is legacy thinking, but I don't see anything wrong with that. If change brings a big improvement, then great! If it's change for the sake of change (or for form over function), then it's bad.
Any user whose existing setup has internal drives and PCI cards will have to (sooner or later) move to external/Thunderbolt solutions or move to another platform. Moving to the MacPro mean not just replacing their Macs but also many of their (costly) peripherals. There's still a limited number of Thunderbolt devices out there - so the devices they need might not be out there - and what is out there is generally more costly. Sure, dropping the legacy ports on the iMac really helped push the adoption of USB; but the MacPro is a much more marginal device. We're still talking about much smaller volumes.
Then you have the external clutter with the extra Thunderbolt & power cables; and the extra power-points required in your workspace. And as awkward as the old MacPro was, I'd much rather lift that from one desk to another than a new MacPro and a handful of external devices and cables.
It'll be interesting to see how Thunderbolt devices stack up against their internal expansion bay/PCI slot equivalents.
So, IMO it's potentially a lot of inconvenience, with little gain. Other than "It's a very cool, tiny box", and "it's new, so it must be better", neither of which means much to professional who's just looking for an upgrade path.
I do understand that for some, this machine is ideal. The only thing that'll probably stop me getting one is the price.
I think that the new forward thinking design may actually move the MacPro away from the margin. That will encourage the development of more peripherals.
I'll jump on the comment about clutter too. This is a desktop...that means you set it up and it stays where you put it. I can't believe a complaint about this machine could be that it is not portable! If you want portability we have the laptops...and NOW that you have switched to thunderbolt outboard gear you can move your peripherals to your laptop!
I mean really, you move your current Mac Pro around? With the monitor(s)?
