If it's like the switch to Intel then it will be $999 and you have to return it when the real versions come out but you'll get a replacement with one of those real versions. Except with the Intel switch you were shipped a slightly repackaged beige box... and that was 15 years ago so my guess is $1499.
And you most likely will have to be an established developer, meaning you’ll have to have an app in the App Store. Apple’s not gonna give these to people that just want to play around with a new machine.
"Submit a brief application for an opportunity to join the program. Selected developers will receive a link to order the Universal App Quick Start Program from the online Apple Store. Priority will be given to applicants with an existing macOS application, as availability is limited."