OK, I think it'll go one of three ways:
(1) Low number, under 100K -- they won't announce anything.
(2) Over 100K but within anticipated 2017/2018 production numbers -- they'll announce something vague like "Over 100000 people have already reserved the car sight unseen"
(3) Really huge numbers -- they'll announce "We are floored by the amazingly large number of reservations, over XXXX, more than we were originally intending to produce by the end of 2018. In order to make sure more of you can get the car by 2018, we are going to accelerate our plan to build factories in Europe and China and we will expand Gigafactory 1 faster. You'll hear more about this in the coming weeks."