My crystall ball is history. Future behaviour is past behaviour. Apple´s track record in these things isn´t very good.
A giant cloud of smoke.
Apple's track record on not repeating major failures is rather good. It tends not to happen. Tim Cook mentioned in a conference recently ( or last Quarter results call ) that if he had to do over again he would have held off shipping the iMac till Janurary when higher likelihood they could have kept up with demand. ( Read inbetween the lines there they launched knowing they weren't really ready just wanted to hit the same date at iPad mini.). It is actually not very likely they will repeat that mistake again.
Apple gave themselves all of 2013 to ship a Mac Pro. That broad window isn't going to be hard to hit if there is a minor 1-2 month glitch somewhere if they had initially targeted July-Sept time frame. Even two month slide is still November.
Besides the super-quantity shipments of iPhones (which pragmatically really can't ship on day start taking orders due to sheer volume) and the iMac everything else shipped in 2012. So what track record? 2011 ( again iPhone and initial launch ramp up for iPads ) what track record?
The only similarity to the iMac is that Apple turned off the "old" iMac production too soon and there were no iMac to be found. They pragmatically shift alot of demand out of Sept-mid Nov into December and hand troubles selling to everybody ( some got shipments , but many were waiting).
Same issue here. While the Mac Pro is much smaller user base shipments to EU Markets have been cut off for months at this point. The Obsorne Effect sends a every larger number of people to the sidelines each month as the year progresses.
Most likely Apple won't completely turn off old factory for new factory this time for a smoother transition but Apple is OCD about "extra" inventory so they won't overlap.
So any BTO config shipping in 2-3 days likely won't be true. But zero machine shipping to nobody .... that likely is not true at all.
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No way will it be possible to have engineered, built, tested en produced in huge amounts new Mac Pro's without some form of "leakage".
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Huge amounts relative to what? BubbaGump's corner PC hotrod building shop? Perhaps. But for the price range $2,500+ the annual run-rate is likely in the 100-250K range. If they had 20K ready at launch that is more than plenty. If the factory can do 10-20K per month you just need a 1.5 month at normal capacity to stockpile that many. If they just ran just a month in advance, they could still launch with very tight constraints for about 2-4 months.
This is a far different context than iMacs or MBP that run 5-6 times as high run rates per month.