If landscapes are your priority, full frame is your friend. The first time you pull up a D800 file in LR, you'll know what I mean. To steal a line from our motor vehicle enthusiasts, "There's no substitute for square inches."
You just don't want to make it easy, do you?
This being said, a D7100 has more DR than a 5DIII that many people use to shoot landscape successfully, so it can clearly be done with Nikon DX. DX having more DoF is in fact a better choice for some landscape applications.
The problem with DX is more the lack of high quality lenses, but it seems Sigma may be picking up the ball Nikon seems to have dropped.
Yep, you put the finger on it.
As I said, I can find reasons for any combinations but to keep it simple and to be done with (for now) I'm 90% decided on D7100. As I will take shots of my kids also supposedly I can justify better focus comparing to D600. An OMD with the Panasonic 13-35 2.8 gets similar resolution to my 16-85 (on D7000) until 70 mm equivalent where the Panasonic has a small advantage.
The main thing that I will be missing with the D7100 and the current lenses is some weather sealing.
To put it perspective:
new D7100 + micro 85 to the current system would cost me 1625
$ for a total weight of 2800g
(excluding flashes, accessories, etc)
new m4/3 system with OMD would cost 4600
$ for a total weight of 1970g
an FX with D600 and mostly new lenses would cost 4400
$ for a total weight of 3350g
a Fuji X with XE-1 and most of their lenses would cost 3350
$ for a total weight of 1900g
(big sales now).
Couple of observations from the above numbers:
- a disturbing one: a m4/3 would cost me more than a full frame
- an unexpected one: a Fuji X would weigh the same as a m4/3
PS. I forgot to add I don't currently print bigger than 13x19, and I don't expect printing bigger than 17x22 in the future