Could there be a radical case redesign?
The current case is just a progression of the G5 case with more internal storage using room that used to be for the cooling system and irronically, it's current cooling system doesn't please the Europrats one bit so they need to redesign that too.
The Motherboard has seen little in the way of changes since the original Mac Pro apart from bus speed increases because it has redundant RAM slots and only SATA 3Gb/s.
The new Mac Pro will have to include the features of the rest of the range because I'm sure the Xeon series are literally the server grade version of whatever Intel have out in their Laptop/Desktop ranges at the time.
This means it should have as a bare minimum, updated I/O such as Thunderbolt, USB 3.0 and SATA 6Gb/s. It wouldn't kill them if they started including several 2.5" bays for SSDs without using adapters or 3rd party solutions too.
There's a system Barefeats reviewed that indicates what Apple "could" be bringing out simply based on the Xeon chips available they could base it around:-
http://barefeats.com/sandy01.html