You may very well see haswell macs prior to another mac pro update. There's little reason to believe otherwise.
I wouldn't bet on that.
There is a reasonable chance that E5 Ivy Bridge will hit "end of 1st half" and that mainstream Haswell will slide to "2nd half".
For the E5, Ivy Bridge is primarily a shrink. Mostly the same architecture on a smaller process. That process is the same process that is being used now to make the Ivy Bridge mainstream processors. So by next May-June it will be quite mature. The E5 dies are larger, but after over a year of production that should be almost a "no brainer" on that process.
In contrast, Haswell is a new architecture. It has "transactional memory" instructions that have never been implemented before. An new updated GPU design. Intel will be rolling out an "SoC" version where the chipset logic is brought inside the package. There are lots of things that could produce some "show stopper" bugs that might cause the schedule to slide for months ( socket change, chip set change, instruction changes , etc. ) The E5 roll out is only the most recent example of that (reportedly bugs found in chipset late in the process). The mainstream support chipset for Sandy Bridge also had presented show stopper bugs that caused a schedule slide.
The likelihood that Haswell will cleanly avoid some major bugs is definitely not zero. Intel might go cleanly this time, but it is probably a coin toss.
That may be one reason why Intel is being coy with the Ivy Bridge E5 target date. If Haswell slides then Intel is going to need another revenue boost earlier and may just slide the E5's up into earlier in 1st half 2013. (assuming it also doesn't have bug, but that is pretty safe. No new chipset. And samples are already floating around so testing is already started. ).
There is some evidence that is what Intel did this year. The E5 roll out slid, in part, to fill the gap created when Ivy Bridge Core i product slid out of the early quarter this year. Intel chirped about "great" E5 sales in their last quarter call. (the Ivy Bridge had largely slid out of the quarter.) If Intel had ramped E5's in late Jan - Feb then there would been a bigger gap between those two launches.
The world economy is so sluggish for the forseeable future and AMD is so far behind in top end server chip performance that Intel is pretty free to move Xeon updates around one or two quarters if they want (assuming have bugs out and ready to go.)
HP's Z1 basically tops out at the fasted quad cpus, but they still offer display upgrades that are compliant with their dreamcolor calibration system. Their gpu selection includes a number of mobile quadros.
Those are external displays on the Z1. They, for the most part, work with the current iMacs also.
If Apple did a "iMac Pro" it should not be too hard to mount mobile quadros onto the motherboard in a similar fashion that more mainstream AMD/Nvidia GPUs + VRAM are mounted now. Although, once the mainstream mobiles are bumped to 2GB (or more) of VRAM there isn't much of specification difference in the fundamentals. It is more of getting into the support certification matrix (for which there are other ways for Apple to fix that; namely point to numbers sold and ask software vendor if they want to miss out on that. )
