Assuming thunderbolt is fast enough? for running graphics cards etc with an external enclosure then a new iMac with 2 TB ports is theoretically as or more expandable then current mac pro's....
Imagine a setup where you bring your MacbookPro home from the field, plug it in to thunderbolt and it connects right up to your Raid, monitor system, RR, graphics card etc. etc.
Why limit yourself to a box with 4 PCI slots ;P
Dunno how realistic, but something to think about....



