I'm quite happy with the 22mp of the 5DmkIII, which may come as a surprise since I'm a landscape photographer. A bump in resolution would be nice, maybe up around the 28-32mp range, but I'm not going to get my knickers in a twist. What I'd really like is better DR and ISO performance.
However, it's difficult from a marketing perspective. Nikon and Sony have their big megapixel monsters with the D800, D810, A7r, and A7RII, and have been rocking three of them for years now. So for Canon to not break the 30mp mark for the 5DmkIV or the 6DmkII could be a problem in the eyes of the buying public. Even if Canon goes with the "focusing on IQ" thing, it doesn't look good to potential customers when Sony's 36mp sensor for the D800, D810, and A7r gave you the resolution without sacrificing the DR and, indeed, giving better DR. Why go with Canon and sacrifice resolution for IQ when you can get both and sacrifice nothing by going with a Sony sensor? (I know it's not that simple when you dive into things, I'm speaking from a marketing perspective. Even a completely brilliant camera may be difficult to market if it's not what the buying public says/thinks it wants)
A bit off topic:
I'm thinking Sony has the right approach here with the A7 line: put out three cameras at the same tier but each geared towards something different. The A7 is the all-rounder, the A7r is the MP monster, and the A7s is the low-light king. Canon's approach of having different tiers (1D, 5D, and 6D) may be part of the problem, as the sprinkling of features across multiple bodies and multiple tiers is a bit of a confused approach to take. From a psychological perspective, the 6D is lower in the lineup than the 5D or 1D, so people may think it's a worse camera. So even if you give something unique to the 6D, it may not attract buyers because of that perceived stigma of being an entry-level full frame body. Maybe it makes sense to have three bodies that are largely identical but offer different sensors? I have only questions, not answers, but I do think Sony is on to something with their A7 approach.
There might be a way to incorporate this approach into Canon's lineup. Have an 18-22mp range for the 1D and 6D lineup, using potentially the same sensor with a focus on low light and DR. If you need low light and high burst rate, go with the 1D, but you only need low light, go with the 6D (and dumb down the 6D a bit to bring down the price and keep it as an accessible/entry level full-frame option, like not having the best autofocus system). Have the 6D as your A7s rival and entry-level full frame. The 5DmkIV is your all-rounder with 24-32mp range (the A7 rival) and the 5Ds(r) is the mega pixel monster (the A7r rival). However, I don't have much confidence that Canon would do this, as offering a variety of products to suit differing sets of needs often bows to trying to get you to pay more for the next model up by deliberately dumbing down the lower models TOO much. Either that, or have three different 5D cameras like the A7 line (but then it gets costly and you risk having TOO much on the market with five full frame cameras, which makes it harder to sell enough units to be cost effective )
A perfect example of this is Canon's treatment of video. Canon seems to insist you pay thousands of dollars more for what are pretty much standard features on cameras that go for a lot less (no point having a camera that A) has major selling features others offer for significantly less and B) most people won't be able to afford anyway), and I seriously think they're losing out on a lot of sales by putting in a half-assed effort to compete in the enthusiast video market. They really need to get their heads out of their asses on stuff like this. It may have worked when Nikon was their only real competitor, but Sony, Panasonic, Samsung, and others are all offering some stiff competition, particularly on the video front, and adapters for mirror-less make switching systems but keeping your lenses a snap, like the A7 series.
