VG247 source. The insider also claims the 16GB version is real (and not a typo for 160GB), using flash memory. There is also mention of a potential PS3 price drop following an official announcement.
The Sony press conference at Gamescom had been used several times in the past for big hardware announcements. The PS3 Slim was officially announced there in 2009, as was a console price cut last year.
That leaves Sony with the 2012 Tokyo Game Show press conference if it plans to announce the new model with pomp at an established show this year.