Pardon my ignorance, but what would be the point of a tilt-shift lens with such a long focal length?
If a whole building can be covered by a 135mm lens, I'd imagine a somewhat shorter focal length and moving the camera up & down with the tripod's central column.
For macro, IIRC neuro has written the TS-E lenses would need an unrealistic tilt range.
Product photography, a cereal box is just like a building, but if you want to see the top of it and not have keystoning you need shift, same for watches, tilt so your plane of focus is on the watchface, arty falloff everywhere else but you don't need the watch to be perpendicular to the camera.
As for the tilt mechanism, that has always been Canon's weak spot, besides 8º it nowhere near enough for a 135mm tilt lens, it will at least 20º to compete with movement cameras (though I doubt it will get it) also the tilt mechanism needs to be geared much better so finer adjustment is possible. As for the current mechanism being unreliable, I'd argue that, the only people who breaks knobs off them are the people too stupid to take the locks off, they are easy to break then, but still need a lot of force.