The k-1 is a great camera that offers much more than its rivals at a better price. True that Nikon or Canon etc have more lens choice, but that only means they offer more things that you won't need.
If you do landscape I would guess the onboard GPS would be useful, as would the pixel shift. That lenses and bodies are weather sealed is also a plus.
Pentax primes are excellent, their Limited series is superb but the rest are also impressive. The 24-70 f2.8 zoom is as good as the Canon and much cheaper, and you can always resort to manual classic PK lenses. I use a Tokina ATX pro 24-40 and the old Angenieux designed 28-80 2.6/2.8 and find them addictive.