I was really concerned about the lack of low-pass/AA filter on the K-5 IIs when it first came out because I've been shooting digital for more than a decade and remember messing with an old 6MP Nikon DSLR that had the AA filter removed by a company that offered this service for photographers who wanted the best possible resolution from their cameras.
Back then, the moire for the 6MP sensor was TERRIBLE when the AA filter was removed. "Jaggies" were also a major problem (clearly visible in hair or diagonal lines of buildings) when the AA filter was removed from the old 6MP sensor.
With that experience under my belt, I was certain that the K-5 IIs would have similar problems ... but I was wrong. The K-5 IIs and K-3 deliver fantastic detail and you either have to photograph close-ups of colorful bird feathers or really have to go out of your way to create obvious moire or jaggies. While I still have some cameras with AA filters (Sony RX1) but I think I will always choose to purchase cameras without AA filters from now on.
I won't burden your bandwith with a full-res image here, but if I took the image below with my old Nikon D70 which was had its AA filter removed there would have been crazy moire in areas of the blue fabric that are in focus and the individual strands of hair and the angled lines of the sunglasses would have been nothing but jaggies. The K-5 IIs and K-3 can handle this stuff without any problems.
From K-5 IIs: