Again, I have to wonder, why the 6D2 compared to ... say the 5DS series at this point, for cost.
The 6D2 is merely rumored, and those rumors are basically a little more resolution, little more sensitive low light AF, just over a stop better high ISO. Thing is, it can't push the 36MP+ area just yet, at least, not likely, if it wants to truly be able to get the rumored 1~1.5 stop ISO increase, as those pixel sites get smaller and collect less light for the surface area each, and with other sensor designs, the higher ISO performance comes by dropping resolution and increasing pixel size for the surface area (A7S, 1DX, etc).
The 6D2 will be the "entry" full frame for Canon. So they will keep it lagging behind the 5D series (maximum shutter, sync speed limits, FPS, overall number of crosspoints and overall performance of AF, buffer depth & speed, number of card slots, resolution, etc).
Personally I wish the 6D2 would go the direction of pure low light niche, by reducing to 12MP and gaining several stops of ISO performance, pushing lower noise in lower ISO ranges and how it works with long exposure, swivel LCD, internal intervalometer without hacks, improved thermal shielding and moisture barriers (just to build on what they already started), basically be a lot more like the A7S II in terms of ISO & DR, but with Canon's AF system..... but they won't do it.
I guess I would overall think that one going from 5D2 to 6D series, instead of 5DS (by the release of the 6D2 you can probably get a refurb/used 5DS near that cost and have a really great all rounder).