... and only after the 5d4 is here.
Canon cannot update the 6D in a meaningful way without stepping on the 5DIII's toes.
So, next in line for an update is definitely the 5DIII.
The 5DIV might get announced as early as next year, IMO.
Possibly in September before the Photokina show (??).
After that, the 5DIII and 5DIV will sell side by side for a while.
And only after that the 6D will get updated.
In the summer of 2015 the earliest, IMO.