dilbert said:
To throw it out there, if Nikon introduced a variant of the D810 but in a mirrorless (A7RII) form factor, I'd dump Sony in a heartbeat for that (lossless raw files, good resolution, IQ, etc) if there was a metabones adapter for it.
Nikon is way too scared about the future of their established mirrorslapper-lens mount (F-mount) than Canon is about the future of EF. Both companies know perfectly well, that a really winning FF-sensored mirrorles camera absolutely REQUIRES a new native, short flange-back mount. They also should know, that a simple native adapter would easily bridge the gap to their old lens mount, to make the transition easier for their customers. But, they figure, that would cost them a lot more in sales of F / EF lenses. Therefore Nikon - and a good portion of their very conservative mirrorslapper user base (even more so than Canon users!) - can only imagine FF mirrorless cameras with a full-size legacy F-mount up front. Of course this will result in a yellow Nikon camera as attractive as the infamous Pentax K-01 -> http://www.dpreview.com/previews/pentaxk01
;D
Not surprisingly, CaNikon's overall strategy driven by their old-fart ultra-conservative japanese beancounter managements companies is simply trying to delay the total system switch to mirrorless systems for as long as they possibly can, with not much of a plan, what to do once it becomes "inevitable".
Given this mindset I do not expect Canon or Nikon to bring FF mirrorless competitors to the Sony A7 II / A7R II and their native FE lens set in the foreseeable future. And even then it will likely have a lot of artificial "product differentiation" built in, to make it less capable a camera than their top-tier DSLRs. Good thing is, that might give Sony (and Samsung) just enough time to finish off Nikon (and make the Canon camera business a loss leader). That is pure speculation of course, but I'd love to see it happen, simply because it would be a corporate fate so well deserved. ;D