Bound to happen but we're still 1.5 years away from production start so they will still garner more reservations in the meantime. Wouldn't surprise me they'd get close to 800K total, especially after the second reveal when people really see what the final car will be capable of.
It is probably many people like me don't want left in Tesla bank 1000€£$ for 1.5-2 years until the model 3 will be available to buy.
I'm planing saving money including the 1000£ in my saving and when will be good time to buy get small loan and buy the car from Tesla. I think lot of people will start buy tesla when it became available and some of them waiting what it changes in the market in 2 years time maybe Audi,BMW,Mercedes or Porsche give us better car who's know?