Unless I missed it, I don't think they've announced when it will be openly available. It seems like right now they're trying to see what the effect is going to be in terms of earnings, visitors, etc. for a select few to see if it's even going to be feasible as is or needs re-tweaking. It'd be nice if it's soon, it has my curiosity up :). Edited to add -- I see from others that it's expected to be rolled out to everyone no later than June.