Full 1080p Passive 3-D is one of the selling points of 4K. LG and a few others currently have some passive 540p 3-D sets, but the 4K sets will be Full HD 3-D. In fact it is actually greater then Full HD in the traditional sense, in that you get 2 million extra pixels because it would be (3840x1080) vs. (1920x1080) active or current (1920x540) passive. You also have Toshiba and others trying the glasses free 3-D that track the viewers with facial recognition cameras and adjusts accordingly, with the filters on the screen. The results have been less than stellar.
Another possible option is the "Near 3-D" glasses free effect 4K sets created by reality algorithms in sets such as Sharp's ICC-4K. It reportedly recreates the viewing material on the fly, sharpening the focal length of usually blurry background data, giveing the picture added depth and rendering how it would look to the naked eye if you where actually there. How well it works remains to be seen.