If they were expecting part 2 to double the reservations(Elons Tweet), then only a second model would do that (IMO). Simply announcing more details about option packages wouldn't double reservations. I think Model Y will be a lot closer to the Model 3, than the Model X is to Model S. I expect Model Y will just be a slight body variation on the Model 3. Same exact wheelbase, same exact front end, same batteries, drivetrains everything. Just a slight roof extension and a hatch, maybe standard AWD and higher price tag. Slightly less Aero, so ~200 mile range. The Reason why Model 3 is targeting 215 mile range, is that the shared base pack is targeting 200 mile range in crossover version. Though,the surprising results, might make them hold off on part 2, until they feel then need more reservations.