Bob, I thought Koh's or one of the other very High end outfits did a K5. I must be mistaken.
The I 1 has been done in many runs by MG, USH and Sunset. I have picked up 2, basically brand new, at very reasonable prices in the last 2 years. I don't you could sell many if you made another run. Too many used ones floating around.
The Pennsy N2 wouild be nice, especially the later version after the converted to Belpaire Fireboxes.
The M1as were all built with long tenders. I have never seen one with a replaced short tender in a photo. I guess it could happen. The M1 were originally built with short tenders. Then a bunch got long tenders on a later rebuild.
As for electronics, just install what ever you want. You don't need a new loco, just add the whatever control board you happen to like. For you 3 rail guys, it is not any more complicated than changing out a burned out E-unit in a postwar Lionel.