stevec
My "outside looking in" guess; they want to first see how the initial "lottery" folks make out before releasing to the general public. As mentioned above there are reports of issues with Kontakt and Melodyne, neither of which I've encountered so far myself, so that may be why the release date is a bit nebulous. Perhaps they are putting the new system to the test right out of the gate.
Very close to the mark. It's not just a new SONAR, it's a new installation system and store. There are a million moving parts and they all have to work. For example it doesn't matter how good SONAR is if the installation is frustrating. So they're testing the waters to make sure the system can handle it before opening it up further. (And I'm pretty convinced it was indeed a random selection process, or Karyn would have gotten an invite.

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The Melodyne issue seems fixed - I tested a build last night - haven't had problems with Kontakt so no comment there. Also there was an issue with the amp sims. If Cake can push those fixes out with the hard launch, that will convince at least me that fixes can happen faster with the new installation model.