But I have a simple question:
Why can't Rodenstock or Schneider just design a lens like the Canon 17mm TS-E?
Is it now a safer bet to go for the Canon 17mm TS-E + ALPA FPS + Credo 50 / IQ150 Route and wait for the 645 fullframe SONY CMOS?
The Canon TS-Es are designed to deliver no steeper angle than 20 degrees at the image circle edge (which actually is a little bit too much for the A7r, but fine for the Credo 50), the Rodenstock Digarons about 35 degrees (my estimate from the data sheets, have not been able to verify it as I don't own any of the wides), and Schneider being symmetrical have the same angle towards the sensor as the field of view, meaning up to almost 60 degrees for the 28XL (to get down to/below 35 degrees with Schneider you must up to the 72mm focal length).
Anyway I think both Rodenstock and Schneider could design such a lens if they wanted to. Maybe not exactly like the Canon (Canon have some unique manufacturing techniques), but the concept of a heavy retrofocus lens. I'm no optical design expert but with today's computer-aided methods I don't think it's that hard to do, what makes optical design difficult is to choose appropriate tradeoffs in the design, to balance conflicting goals.
If you would want to make a lens as sharp as the current Rodenstock Digarons (note: Canon TS-E II lenses while good is not as sharp as the Digarons), but change the angle from 35 to 20 degrees, you would get the problem that you need even more glass elements, and still the barrell distortion may increase, and to counteract that you would need even more glass. You would end up with a lens heavier than 1kg, and a normal Copal shutter would not be able to support that so you would either need to use an oversized Copal (with slower shutter speed etc) or make some new shutter.
Normal wide angle lenses that cannot be shifted has the advantage that you can apply lens corrections in the raw converter, and most modern lenses are designed for that. If you turn off lens corrections the Hasselblad H and Phase One 645DF wides will show quite some chromatic abberations, ie they have made simpler optical designs and correct them in the raw converter. Tilt/shift lenses don't have that luxury, they need to perform without lens corrections, and users expect them to perform
better than the corrected MF-DSLR lenses.
The ability to do that has been based on the optical design formula tradeoff that you don't need large aperture and you can have steep angle towards the sensor. Making the lenses more and more retrofocus take away some of that, and the only way around that is to make an extremely complex design, which of course would mean a very expensive lens, and a very heavy lens, and making it unfeasible to use the traditional shutters.
So it's just way better to get a CMOS that can handle steeper angle... if I were Schneider or Rodenstock I would sit tight for a while and hope that it will happen.
A comparison example: the retrofocus Rodenstock Digaron-W 32 has 14 lens elements and weights 800 grams, the symmetrical Schneider Digitar 35 has 8 lens elements and weighs 240 grams. A new 32 with more retrofocus would have even more lens elements and weigh even more (and cost more) than the current Digaron-W. Already the 32 has problems with loading the Copal shutter too much so it's very delicate, more than one have got their lens bent at the shutter just by setting down the tripod a bit too hard.
Zeiss Otus series is another example of what happens when you take the optical design to an extreme, the 55mm lens weighs 970 grams and has 12 lens elements which is a lot for a 55mm lens and its small format image circle. I'm very curious how a 24mm wide angle in the Otus series would be designed...
Keep in mind that 17mm and even 24mm on a 44x33mm sensor will be extremely wide angle. Some indeed like to shoot with ultra-wides, and in architecture you may have no other choice in some situations, but I think for landscape photography you get nicer perspectives if you don't go wider than "24mm 135 FOV", ie about 31mm for a 44x33mm sensor and 38 for full-frame 645, with shift available you can go a bit narrower still ie Digaron-W 32 for the 44x33 and Digaron-W 40 for the full-frame 645. For the 48x36/49x37mm sensor size 35mm is quite nice, and indeed that's my widest lens currently.
As things look today, Alpa is probably the best tech brand to go for when it comes to adapting to future changes in lens/sensor combinations. Arca-Swiss is also pretty strong (the Photokina 2014 product releases showed that they can do electronics too), while Cambo lags and Linhof even more so, as they don't have the same ability to make electronics, at least not yet. I have still have no problem with using Linhof "old school" design, as I like that type of design and if tech cams will change direction into a boring oversized A7r type of design I will most likely drop out of tech cams when it's no longer possible to continue the traditional way. That dark scenario would still mean that I have 10 years of Linhof shooting ahead, only when my Copal shutters fails and I can't have them repaired or replaced and my digital back fails and I can't get it repaired or replaced with a something compatible with symmetrical lens design that journey will end.