Well, we have some numbers. Thanks to HTC employee, Shen Ye, it's been revealed that 15k of the devices were sold in the first 10 minutes of the device going live. He tweeted:
Woah, more than 15k units in less than 10min :o
— Shen Ye (@shen) February 29, 2016
Important to note, none of these headsets are 'sold' yet. The pre-orders don't actually take your money until the devices are ready to ship, so all kinds of shenanigans could happen to any number of these orders.
Still. It's pretty impressive number for a device so expensive, that is no doubt.