My wife wants a Model X. Practical ride height, loves the auto opening/closing doors and massive front panoramic windshield, wants a larger vehicle for road trips so a Model Y is not a consideration.
Whereas I want to trade our 2013 S for another Tesla S (preferably P90DL but it's all up for negotiation), the reason I don't like the X is predominantly because of the look, I'm a car guy (you'd never know it from my Smart ED, but it's RWD and fun to drive, but I digress) and really didn't like the Mercedes SUV she owned before the Model S.
Meaning, Model Y will probably sell in ridiculous numbers, to all sorts of people that want 1" more ride height, 1" greater tire size, and a hatch back. I don't personally get it, the Model 3 is apparently 70% shared content with the Y, but there you go, it's all subjective and depends, sedan format is going to sell well, but "SUV" (in quotes) format will sell better.