The concept of a tiny, high resolution camera with excellent small lenses for landscape photography is very appealing. However, here are some of my thoughts on this.
First, landscape photography means tripod. This already weighs you down to the point where a tiny difference between a 5d MkII and M9 becomes irrelevant. If you shout out of hand (as most Leica shooters seem to), that's all fine, but then forget perfectionism of resolution, forget blue hour and forget blurred water, which all in all means forget most of landscape photography.
Second, with Leica you use primes, which is all great but my experience is that in landscape photography you sometimes don't have much choice in your position, and a short tele-zoom is what it takes to get that perfect shot of mist in the canyon. Zooming with your legs is a nice sound bite, but in reality it results in lost opportunities.
Third, shooting with a polarizer with a rangefinder is a huge pain. Shooting with a polarizer and ND grad cokin plates even more so.
Fourth, not all the things you see in nature are landscape. Sometimes you need a closeup shot of that hummingbird and with M9 you can kiss it goodbye.
Fifth, sharpness. You don't usually shoot landscapes at f/1.4. In fact, my usual stop is f/13, which gives me DoF without losing much to difraction. All my Canon lenses are perfectly sharp at landscape stops. If there's a problem I don't have with 5d, it's lack of sharpness.
Sixth, Leica users talk much about a huge SLR and a huge bag of lenses as their demon sheep competition. Sorry folks, but I usually have one lens on the camera, another one in the pocket along with a spare battery, my wife carries the tripod and off we go. It's not like I'm carrying an elephant. OK, if I'm riding a bike for 40 km, half of it uphill, then I feel all the weight, but that's where I wouldn't carry my tripod, either, and if I wanted a camera for that, it would be something along the lines of micro 4/3, because an M9 wouldn't really fit into my jacket because let's face it, it's really not all that small.
So Leica, to me, just isn't practical as a landscape camera.