My opinion:
I too think P85Ds ans another Model S Ds are behind the resurgence of the Update button. I am fairly certain, judging by the nature of other high-tech releases with pre-orders, that a significant amount of people were in this for the newness of the AWD Tesla thing or otherwise in it for AWD more so than Model X. Thus Model S AWD coming out sooner will get some of these people - just like Model X AWD coming out sooner would have done the reverse and eaten some Model S D purchases.
Early adopters (and that's a lot of the Tesla Sig folks) like to buy the latest and greatest and now Model X pre-order got superceded by Model S AWD, so attention moved there. It may reverse a little once Model X is produced and again the latest news instead of a pre-order limbo like now.
People like the Order button more than the Pre-order button. What is immediately (relatively speaking in this case) available is more attractive than what is not, to an extent at least. Very true for many products and just human nature.
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Why would it say deliveries begin 2014? That seems to counter the guidance we've been hearing.
Is it possible Model X Sig deliveries for the very first few might still commence in 2014? I mean, Tesla is clearly keeping the lid on the Model X ordering process - until a moment in time when they no longer are. It isn't completely impossible, I guess, that Model X orders might go live (in batches based on priority), say, 1st November for December 15th delivery in the U.S.? And then ramp-up so that new production orders are delivered fall 2015.
People who have been following this more closely may offer better insight, but just because Tesla is silent, does not mean Model X couldn't come out very soon?