GTRacer pretty much said it as it is, if you have something to film now, get one, otherwise you may as well wait.
It does appear that a release date/announcement is now tentatively being scheduled for October, which would make sense as that's the date the last two models have been announced.
But going by the Hero3 Black launch which was more significant, it was announced in October, but didn't start shipping until about December. There was really limited stock of the cameras and it's new accessories before christmas and most who wanted one couldn't get hold of them until the end of January. So that's certainly wroth baring in mind if you do wait, that even if a new one is announced soon-ish, don't expect to be able to have it right away.
They are touting proper 4K is likely on the next model, but personally its the rumoured 1080p@120fps and 720p@240fps that interests me the most. Better battery life is really what it needs though, as it's never been as good as the Hero1 & Hero2 models.