The 5D4 has very impressive high ISO cleanliness even though it maintains a large amount of low-ISO dynamic range. Also, Canon is conservative aka realistic with their ISO ratings unlike Nikon. This is why the 5D4 appears to have a lower max native ISO. But in reality, it produces more usable higher ISO images.
I think in this generation, the 6D2 will not be that much better if at all over the 5D4's sensor. Sure, maybe a little bit on the ISO if you pixel peep to the extreme - but the higher rez will probably make up for it once you clean it up in post.
Larger pixel wells I don't think will matter that much on these newer sensors unless they are significantly larger (as in a 20mp or lower sensor), 30mp vs 26mp should be meaningless.
They did say all new design, so it is possible that some refinements and/or new tech is in this sensor that can make more of a difference - but I'm merely guessing that won't be the case. Pixel peeping level improvements, ok. Obvious, practical improvement - no.
The cameras that really need the new sensor tech is --
7D2, a 7D3 should be the higher dynamic range, better ISO sensors without AA filter. This would be a huge win.
5DS/R - these don't need high ISO, but they need tons of dynamic range. If Canon can tune that sensor for maximum dynamic range, this becomes a big, big win too. This camera is not for event shooters or low light. ISO 6400 max is fine. Go for the big DR where it matters on the lower ISO ranges and studio / landscape people will go crazy over it.
Reason I bring these up is -- the most exciting stuff coming from Canon is updates to those cameras, not the 6D2 which is a turd, or the 5D4 which is a great camera but a jack of all trades, master of none. However, it will probably be 2018 before we see any update to either.
The only nice thing about the 6D2 will be that it is a preview of the matured sensor technology of this generation that will make it into the 7D3 and 5DS/R II.