Nice surprise would be to replace one of the OB with 4 sleds for 2.5" drives. 4 * 2.5", and 4 * 3.5" would be a very easy, cheap and significant "upgrade" to the basic design.
8 is likely too many. 6 would be a step up, but still make a larger group of folks happier.
Two issues bandwidth and thermals.
Bandwidth
" ... a baseline –A model with four SATA 3Gb/s ports and six SATA 6Gb/s ports, four of which are tied to the SCU. ..."
http://www.tomshardware.com/reviews/xeon-e5-2687w-benchmark-review,3149-3.html
Apple is likely using the C602 ( -A model) version without SAS support so can use the 4 connectors on the SCU as 6 Gb/s SATA. The non-SCU portion of the chipset only has 2 6GB/s SATA units. The other four at 3GB/s.
If Apple attaches the SCU unit to the 3.5" drive sleds. Then there are only 2 6Gb/s SATA channels to hook to. I doubt Apple would play the "mix and match" design where somehow have to make a distinction for users. The majority of 2.5" drive users are going to be SSD folks. Most of the SSDs folks are going to be using over next 4-6 years are going to be 6Gb/s variants. So just 2 sleds for 2 6Gb/s connections.
If Apple uses the C604 ( -B model ) they would still have SAS ability in the 4 3.5" sleds for folks moving old SAS drives up that were using the RAID card in that configuration. But they are still capped at just 2 6Gb/s SATA connections. That also would probably cap any additional 2.5" bays at two.
I think they won't use all of the SATA connections. That's alot of traffic to pump through the chipset if also have low latency traffic of USB 3.0 and Firewire 800 also pumping through the same DMI link. The problem with the C600 design is that can oversubscribe the the link. The 606 and 608 ( -D -T) versions obviously do it (i.e, need for x4 PCI-e side channel to CPU), but the others also if fully leverage the 8 PCI-e links also hanging off the chipset with very high speed, low latency I/O .
My guess would be that it would go something like this.
one Superdrive -- 3Gb/s SATA
two external locking 2.5" sleds (**) -- each on 6Gb/s SATA
four 3.5" sleds -- attached to SCU unit (either 3Gb/s SAS or 6Gb/s SATA )
one mSATA card socket on motherboard (**) -- 3Gb/s SATA
So two "left over" SATA connections left unhooked.
(**) both somewhat borrowed from XServe.
External 2.5" sleds are nice if have Mac Pro mounted in an rack swapping out failed HDD without having to unrack the unit. They can also be nice if moving 2.5" drives from camera recorders to Mac Pro .
A small SDD mounted inside the box is good for a diskless server box. [ yeah there is alot of bulk to the Mac Pro to be a diskless file serving box. But it could host PCI-e cards that connect to the storage. Similarly could be host to a OpenCL GPGPU cards as a computational server. ]. It also avoids having the OS/Apps drive on the SCU if have all drives stored internally with no external access . Also, some folks won't like even lockable external sleds.
If Apple wanted to kill the remaining Superdrive , then perhaps a SATA USM interface. SATA USM modules haven't had much uptake (Seagate GoFlex only major usage so far), but that might be good for one more external "drive socket", but not sure if they'd want to put that on the core chipset controllers. eSATA also is somewhat better isolated on a discrete controller if they even went there. Extremely doubtful they add a SATA controller if they put Thunderbolt on the box. Just plain doubtful they will add a SATA controller on even if they don't.
Thermals
8 drives is a significant amount of heat to get rid of. It isn't like the GPU and CPU are getting significantly cooler.
Plus there is pressure to shorten the case a bit. The Mac Pro has "front to back" cooling. If decrease the frontal area then gets harder to use larger, slower fans.
I think Apple will move some of the 3.5" sleds around to the old ODD space that the two 2.5" drives sled don't move into. That shift will be to do something more in the thermal/power control. In turn, opens the thermal envelope for some hotter GPU cards.
Opening a window for two 190W cards would probably be better than two more drive sleds. If folks really need "bulk" storage in the short term that actually better to do outside the box. High speed, low latency GPU access is much harder to move outside the box.
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I was more excited before I read Cieplinski's blog.
Apple could release on Tuesday like any other Tuesday when they usually do with press releases. That the "whole show" was going to be warped into a Macworld..... that never was the case.
The vast majority of developers who are at WWDC are there for iOS6. That has little to do with Mac releases. Mac releases have slide to June because Intel (and AMD/Nvidia ) slid hardware into late Spring. They just happen to be around the same time. Apple reserved the date for WWDC long before Intel's roadmap went slid almost a quarter along its timeline.
There was no long term plan to make this WWDC a "MacWorld".... so it likely isn't going to be a "MacWorld". That doesn't mean new Macs aren't going to come out when the parts and software are ready.
