^ There are already some "prototype" applications out on the market. For example, Candy Crush on WP was allegedly ported to WP using Islandwood. So, first products have already existed for quite some time (as part of MS' bridge development projects)...
I've not yet heard of any specific release date. MS surely has timeframes and goals set, but MS would be stupid to make those public, as it's almost impossible to accurately plan projects like these out to their completion, and anything they say would instantly be labeled "a promise".
In the latest askdanwindows he "guestimated" Astoria would go public around Q1 2016. No word at all on Islandwood, which is the FAR more interesting project of the two, but for some reason gets almost no press coverage.
Anyway, sorry, no specific dates...