For starters: I have reserved a Model S but now also a Model X. I'm not getting the Model S (but keeping the reservation as long as possible in order to get a test drive as soon as that's possible here where i live - Norway). The X just makes so much more sense - AWD (crucial in our long winters), more family oriented. The big draw-back of course: 1 year (at least) longer wait! That sucks.
But when thinking of the longer wait maybe there's an upside, i.e: maybe a new battery tech is introduced and the best battery may not be 85kW but rather 100+ kW??? How probable is that? I know that the Model S uses the Panasonic NCR18650 cells. I know the cells used in the Roadster were 2200 mAh (3.7 V) and we know that resulted in a 53kW battery. Now i know the Model S/X platform is larger and hence a larger battery but the big change is the new type of Panasonic NCR18650 celles used: 3100 mAh (3.6 V) and we all know this gives us an 85 kW battery. Now think of the time passed from the Roadster to the Model S. And think of the fact that the latest Panasonic NCR18650 cell is not the 3100 mAh but one that is 4000 mAh rated at 3.7 V. Tesla has not gone for this new cell in the Model S I guess since it's so new and it's not just like you pop another cell in the battery pack and then you have a new, better, pack. But it a way it's like that, isn' it?
(Those who want proof of the 4000 mAh cell can check this link: http://www.amazon.com/UltraFire-Prot.../dp/B006OHO9I2 where theyu're selling small packs with this cell, for use in flash-lights, lasers and such.
So, it's inevitable that the packs will continue to evolve, and it would seem that Tesla has a good partner in Panasonic and I wouldn't expect them to switch, since Panasonic seem to be at the forefront of battery tech. The the question is how likely is it that once the Model X (and maybe also the Model S 2.0) is produced in another 1.5-2 years time will there be 4000 mAh (or even more) in each cell? If you switch out a 3100 mAh cell with a 4000 mAh cell rated at almost the same voltage it gives an aproximate 110 kW pack (disregarding any weight difference)!