@Ian2: Well, there's only a little people who participate in WP Apps development here. The user based would be too small if you limit it to "long term Niners".
On the other hand, ship it to "long term dev center account holders" could have make more sense, but that'll roughly be meaning the same thing as people who "Developer Preview" unlocked their phone.
Btw, I'd like to hear what will be the expected lowest spec. of phone that will be allowed to run this feature. My Lumia 920's screen have grown significantly yellow and I'm considering replacing it some later time. Will Lumia 940 be enough to run it or do I need to wait one more version?