As a landscape shooter who bought into digital with the 5D2 (since it was then able to outshoot colour MF film), the A7rII is probably the best successor to the 5D2 out there.
It has the best image quality of any non-MF body out there. AF with Canon lenses is similar to the 5D2, although, unlike the 5D2, more than the centre point is usable. The single SD card is disappointing, but not a deal-breaker for most (anyone know of a lightweight device that can copy SD cards while on the trail?). Battery life is not great, but you can carry 2-3 Sony batteries in the space/weight of a single LP-E6. In short, it performs just like a 5D2, but with a much better sensor. Sure, AF is not great (relative to top-end SLRs - relative to other mirrorless bodies it's amazing) but no-one ever bought the 5D2 for its AF either, and, when shooting landscapes you'll be using MF anyway. If you use it in the same way as many people used the 5D2 - as a body with a best-for-its-time sensor, for the utmost image quality without needing much in the way of other features - you won't be disappointed.
Considering the alternatives, the 5D3 doesn't really improve on IQ compared with the 5D2 and the D810 can't take Canon lenses, so neither are really much of a successor to the 5D2 in terms of being a high-IQ, high-resolution, Canon-lens-compatible camera for shooting subjects that don't do much. Each has strengths in other areas (notably AF for the 5D3, and just being an all-round kick-ass camera for the D810) but neither really improved on the 5D2 in terms of what they offered for that core group of 5D2 users (the D810 being a non-starter for those heavily invested in Canon lenses). The 5Ds is a true successor, but the sensor doesn't quite match that of the A7rII, although it comes closer than any other Canon sensor. So, for the purposes of shooting nonmoving subjects with as great an image quality as possible, it's hard to beat the A7rII at the moment.
Incidentally, though, the 5Ds may just be the best *wildlife* camera on the market at the moment - with top-level AF, a full-frame sensor and the pixel density of a crop sensor, it allows for fantastic cropability, in effect turning every lens into a 1-1.6x zoom lens (if you consider the crop sensor area the minimum acceptable size for image quality) and making for much easier framing while shooting. Also, since there's very little overlap between wildlife lenses and landscape lenses, it becomes perfectly possible to run two separate systems side-by-side at no greater cost compared to using the same system (e.g. Canon or Nikon) for both. 5Ds, 200-400 f/4L and 600L for wildlife, plus A7rII (or D810) and your choice of shorter-FL lenses for landscape, costs much the same as running an all-Canon or all-Nikon system with the same focal length capabilities, but gives you better results.
I'd still like to see what Sony has in store for its 'pro-level' E-mount body, though - dual card slots, lossless RAW, even better AF (maybe 6D or 5D3 level using adapted lenses) and a bump in resolution to 54MP would be high on my list.
