"Microsoft will be holding a press conference at gamescom next on August 17," reports VG247. In this regard, Microsoft "sent out invites to a gamescom "play day" but didn't make it clear if the company would be holding an actual press conference at the German show as it did last year with Lionhead boss Peter Molyneux." Shortly afterward, a Microsoft Representative over phone confirmed that "there would indeed be a full conference during the event at Gamescom and that they had several announcements to make. At the time of the phone call, Microsoft stated that it wasn't yet sure what form the conference would take. It could only confirm that the event would take place on the same day as EA and Sony's conferences."
Nintendo won't be holding a conference at the show.
The shindig kicks off next Monday, with gamescom itself running August 18-22, the first day being industry-only.