The game is playable from beginning to end with developer kits. That means it's playable, so long as you can insert stuff into the game yourself, and clip through walls and fly around. When websites have a link to a beta, and the link leads to nowhere, that means that there is no beta available. Now, or possibly ever. A beta has never been confirmed. Trust me, if Bungie says the game is pre-Alpha, then it's pre-Alpha. Bungie's confirmation is always more accurate than our own speculation.