Blizzard being at Gamescom is in and of itself neither unusual nor unique. Gamescom is just one of those conventions that the company attends, after all. But hosting a separate press conference at the show would seem to indicate that the company has something to announce beyond what fans are already aware of. Which, at this point, would almost certainly center around World of Warcraft.
The last patch of the game’s current expansion is live now, and fans are unsure what the content gap will look like beyond vague promises that it will be shorter than the 14-month gap after Mists of Pandaria ended. Having the game’s next expansion announced at Gamescom in August would be unusual, but it would also contribute to the expansion being out sooner. Of course, it could also just be another Diablo III expansion or some other major announcement, so fans will simply have to keep their eyes open next week to determine the purpose of the mystery conference.