1) Perspective correction is very well possible in Photoshop (or whatever program we use).
Perspective correction in Photoshop degrades image quality, it can also make compsosing more difficult and means wasting resolution because you have to frame your shots with extra space to allow for the post-correction crop. While this might be better than not having the desired perspective, IMHO it's no substitute for getting the perspective you want in-camera.
2) A better alternative may be to stitch multiple photos. Resolution is essentially increased by 50% when stitching as you normally turn the camera along the short side. Modern programs like Autopano Pro using the "Smart Blend" rendering option reduce the need to rotate the camera around the nodal point of the lens, but even with a nodal slider a simple "pano head" and slider fits both your pocket and your wallet, naturally assuming a voluminous pocket and wallet.
An additional advantage with stitching is that you can use a wide range of zoom lenses and that only the central part of the lens will be utilized.
Stitching is no panacea. For one thing there's always the concern of time, and the fact that your scene may not be completely static due to changing light, blowing wind, or moving subjects. There's also a greater margin for error - there's nothing quite like getting home and realizing that you missed the overlap on one shot and ruined the whole image. I've also found that at wider the angles of view, the results of stitching look different than if you just shot the image with a wide rectilinear lens. The projections performed by apps like PTGui and AutoPano pro seem to over-compensate and cause distortions. Finally, you lose the ability to see your composition in the viewfinder.
The "Scheimpflug principle" cannot be duplicated the same way but several pictures having different focus can be merged into a single picture using "depth merge". I have tested this very little using "Helicon Filter" with less then impressive results but I would expect that it is workable with some practice.
As far as DOF stacking, I've found the results to be less than satisfactory with today's tools. For some images it works OK, for others it doesn't do so well and you end up with artifacts or uneven focus.
Stitching has its place, I use it quite often, but in some situations it's best to get the image in a single shot and T/S are one more tool that can make that possible. And T/S lenses are also often quite good for stitching; in their centered position corner sharpness and light falloff tend to be excellent due to the larger image circle. Plus, you have additional options such as using shift for a "flat" stitch, or rotating the camera in the traditional manner while using tilts to control the DOF (only works for single-row panos though).