Indeed. I also replaced my 24mm f1.4 and 24mm T/S by the 24mm f1.8.
I stitch a lot also but have been using a Sigma 20mm f1.4 for cases when stitching doesn't work. The sigma is great as a MF lens, pretty useless as an AF lens on the bodies I own. I intend to sell the Sigma and replace it by the 19mm T/S.
I do not understand your choice completely;
you replace the 20mm Sigma with the 19mm Nikkor.
If the AF of Sigma does not work well let us say it is a manual focuslens as is the Nikkor.
The Nikkor has to be good even shifted so possibly is not as sharp as the Sigma in the central area.
The Nikkor has probably better flare control than the Sigma...
(The Sigma is much cheaper than the nikkor)
From your posts i get the impression that you enjoy absolute lens quality.
It is not likely that you are going to find that on a shifted 19mm image... or Nikon has produced a miracle...
(Also it is more work to correct the distortion of a shifted image)
can you explain?