Sony is planning to officially detail the PlayStation Neo at a New York Event on September 7th, if reports are to be believed.
French site Gameblog is carrying the date. It points out that the PS4 was also revealed in New York, and also mentions rumours of a possible Nintendo NX reveal on September 12th, which if true would certainly give Sony incentive to get word of its machine out first.
On the flip side, The Tokyo Game Show starts on September 15th, which arguably might be a more fitting venue for the reveal? Although with console gaming in massive decline in Japan, perhaps a stateside reveal would be more suitable.
PS4 Neo was finally confirmed just before E3, quite some time after the machine was first detailed in extensive online reports. Sony chose not to unveil the machine at E3, however. Microsoft is also working on an upgraded version of the Xbox One that reportedly packs far more tech power than Sony's machine.
Rumours persist that Neo may arrive at retail this side of Christmas, with previous reports pointing quite firmly to October.