I've been casting around for the ideal backpacking camera for years. It needs to be (my requirements, anyway)
1.) Relatively small and light (2 lbs with lens)
2.) Water/dust/ shock resistant (Nikon AW1 level would be ideal, but the AW1 is too compromised in image quality and usability - no viewfinder, AND the rear screen is unusable in sunlight - for me to consider it, so I'm always short of the ideal in this category).
3.) Image quality sufficient (body and lens) for 24x36" prints.
4.) One high quality lens that covers the range from 28-105 (in full-frame terms), with effective image stabilization (on extended trips, I won't take a tripod, both because of weight, and because it's too clunky to use while hiking.
I've used an Olympus E-M5 while backpacking (took it 200 miles on Vermont's Long Trail). It stood up to the rigors of the trail just fine, but I would call the image quality "almost there". I feel confident printing up to 16x20" from it, but not larger. It also has some dynamic range limitations that can become apparent in smaller prints.
I use a Sony A7r on day and overnight trips, and considered the 24-240 as a single lens option for long trips. The A7r's image quality is, of course, impeccable - that 36 MP full-frame sensor is the current state of the art, short of a Phase One back. It's also sturdy. The problem is that the 24-240 weighs nearly 2 lbs alone, which means that it's going to want the grip in order to balance reasonably. The A7r/grip/24-240 combo is approaching 4 lbs. Early reviews aren't all that enthusiastic about the 24/240, either.
I have just ordered a Fuji X-T1 with the 18-135 at the present low price, specifically for backpacking use. I've used Fuji X-Trans before, before the X-T1 came out, and loved it (very nice cameras to use, and the image quality is very good - substantially better than Micro 4/3), except for the lack of weathersealing (both the X-T1 and the 18-135 have quite extensive seals, but Fuji had nothing sealed until those two pieces). I won't be selling my Sony gear, and I have some Micro 4/3 around for video use and very long lenses, so I will actually have toeholds in all three major mirrorless systems, which is a bit inconvenient, but it will allow me to build up whichever system(s) evolve in my preferred direction.
I hope that one of the following happens, allowing me to simplify my multiple systems.
1.) Fuji releases a weathersealed body in the 24-28 MP range - if the per pixel quality and dynamic range is as good as the existing 16 MP bodies, such a body would be very close in image quality to the A7r, and would let me abandon Sony and go Fuji / Micro 4/3.
2.) Sony releases a body with superb internal video capability (4k and significant slomo, good codec, WITHOUT needing an external recorder). If this happened, I could sell the GH4 and go Sony/Fuji.
3.) (unlikely, because I looked VERY carefully at Sony roadmaps before ordering the Fuji). Sony releases a high-quality variable-aperture zoom that reaches at least 105mm, and is in the 1 lb range. This would remove the need for the Fuji, and make me feel very stupid for adding it!
4.) Fuji releases a body with very good video, which I think is unlikely (they don't seem to care, and it goes against their philosophy). If they did, it might very well ALSO have an improved sensor for stills, and might let me slim down to one system for everything.
5.) A Micro 4/3 body with better than Fuji image quality comes out (I think this is hard, due to the laws of physics, and also to the Micro 4/3 partners focusing on features and video).
With none of the above so far, I've ended up with three systems, Sony for ultimate image quality, Fuji for light weight with very good image quality, and Micro 4/3 for video and very long lenses.