The benefits of the 6D over the 5DII: the low light AF has better performance; the metering appears to be more accurate; the AF may be better; smaller size, if that is important to you; no need to purchase CF cards because it has Micro SD; and the wireless/social media integration, if that is important to you. The ISO performance may be better, but we don't know until Canon opens the camera to reviews. If the camera processes shots as peppy as the 5DIII, then it would be an upgrade from the 5DII.
The 5DII does not have wireless. The wireless app for focusing shots is a novelty unless you shoot on a tripod. I use a similar (wired) app called DSLR Controller when I use my tilt-shifts with my 5DII, but I only use it to help with my hand focusing of the corners of the frame. The whole mobile phone app integration appears to be tailored for the individual that would like to use a DSLR the same way that they would use their smartphone for uplinking shots to social media sites. To me, this adds no value. If that is important to you, it is an advantage of the 6D over the 5DII.
From what I can see from brief hands-on reviews, I would not trade my 5DII for the 6D. I have shot the 5DIII and although it processes shots faster, has an amazing AF system, and has a one-stop ISO advantage, I probably would not upgrade to it either. I am looking to the next gen of 5-series camera.