High res 135 was a big risk when D800 was introduced. Would anyone want that high resolution, or was it just a waste? It became a huge hit though, clearly there was a high res niche to fill, and since then Nikon has followed up with the D810 and Sony has released the A7r. I think it's more about reaching into the super-expensive medium format space rather than to just make high resolution pictures in the traditional 135 genres. In terms of grain-free resolution a D810 can produce prints which is really close to 4x5" large format film. That's cool.
Canon is stable in all the "old" genres of 135 photography which fills the needs of the vast majority of users, but the high res niche remains unfilled. To say that is to "abandon the pros" is a long stretch, but indeed those that did much work with the 1Ds3 probably feel let down when they've seen what's possible with a D810. I guess the best alternative you have as a Canon user is to buy an A7r body and adapters while waiting for Canon to hopefully catch up.
Probably a larger user group than pros that want a high res Canon there's amateurs too. Landscape is huge among amateurs, and that's an application when high resolution is desired by many.