Originally posted by 2351HD I think that certain focal lengths lend themselves more to either tilt or shift.
For example on the 645z, I would take a 35mm (28mm) tilt lens and a 24mm (19mm) shift lens.
You need the depth of field on the 35 and you need the shift on the 24.
Just my preference, why crowd the lens with too many things to go wrong.
May as well make the most use of resources and design a lens that does both really well, since it's going to end up being a rather hefty and high-priced optic anyway. Even if it had a 5.6 aperture, weighed over 1 kilo and would require it's own tripod mount, I think most people would be happy. In fact, I really hope that Pentax make a tripod-mountable tilt-shift so that you don't have to correct for parallax when doing in-lens panos.
One thing I want to point out is that more than tilt, shifting requires the effective focal length and image circle to be significantly larger than the intended format, for instance the EF 24mm TS-E is actually a 17mm lens, while the 17mm TS-E is actually 11mm, if you take into account the expanded field of view from maximum shift. From a technical standpoint, it would be easier to design a tilt-only super wide, as shifting is a pricey commodity.
Every shift lens can effectively be thought of as two lenses; the focal length as you get from one shot, and the effective FL as you can get by stitching shots in-lens, so it would be a very bad idea to strip any such lens of this feature.