Bottom line seems to be this, in the interest of maybe forestalling other such threads (ha!): ASUS is shipping SOME stock to SOME retailers on or before the 19th. So, they'll live up to their public statements. However, they're shipping far fewer units to far fewer retailers than expected. So, only a select few with the right pre-orders at the right retailers (Best Buy and Gamestop, most likely) will actually get Primes before the end of the year.
Pretty much anyone who wants one should be able to get one by, say, February.
I think that's probably as solid a bit of speculating as anyone is able to conduct at this point.