Man, this thread is more bi-polar than ever! So if much of Model X Sig production slips to Q1, that is not brilliant news, but certainly not the end of the world. Ever since Tesla modified 2015 guidance to 50k cars, it was clear X is not going to be a significant part of that. Whether it`s 1400 Sigs like their earlier internal goals suggested, or 500-700 like we are guessing today, still means they need around 49000 Model S.
In Q2 they have guided for flat deliveries in Q3, so I really don`t understand those folks who "knew 2015 will be a miss as soon as Tesla published Q3 delivery numbers". That part actually went according to plan. We may still see a miss in 2015 if S production can't or won't be ramped enough, but it mainly just comes down to this: when they announced the revised target for the year, was X a significant chunk (e.g. 5k) of that, or was that move from 50-55k to 50k an indication of "we`ll make 49-50k Model S and whatever X we manage to get out will be the icing on the cake". I suspect the latter, so if we have a miss it will be by the hundreds, not the thousands.