I think WSJ mentioned it wouldn't start until sometime in the 2nd half of 2015, and that's as narrow a range as I've seen on a date. Doubtless, there will be some units popping up on ebay and the like, and Eremenko specifically answered a dev's question during devcon 2 that there were no real controls that might prevent Puerto Rico modules from working anywhere else, other than the cell radios, so while they are trying to focus on one area for data gathering purposes, there will be leaks. I think one reason they really don't care is that a big part of the market test is drumming up earned media and awareness while the ramp up, because this model doesn't really lend itself to a multibillion dollar worldwide ad campaign that Samsung or Apple would use. There are too many different parties and too many small parties in the mix to effectively promote that way. But every stage of the tiered rollout, including these dev conventions, generates really valuable coverage. I was really impressed with the breadth of coverage off devcon 2, and it isn't even finished yet.
The ebay units won't help many of us though, because there isn't one Ara device. Unless you actually have friends or family there and you can tell them exactly which modules to buy, whatever bundle someone gets and puts on ebay won't be particularly interesting. If you want the full experience of really building a device just for you, you'll have to wait an unknown but painfully long time with the rest of us. Well except djzbra. Ah, why does Puerto Rico always get all the luck