I too really want Scott to do the PA/PB. I have a feeling he just might. It seems to fit his criteria.
PAs are certainly high on the desirability list. A stumbling block seems to be the trucks. They are very expensive to make to 3rd Rails standards. My guess is they are trying to come up with an acceptable way of making them sprung (which is the 3rd Rail standard for all 3 axle trucks) but with the equalizers fixed to reduce costs. Where an E unit truck without equalizers may cost $5 materials and labor to make, a PA truck with working equalizers will cost $25-50 to make (I made up the numbers, it's the ratio that matters). So you are currently looking at a price increase of $50-100 per unit which appears to be out of the current market's acceptability range.
Well, I for one would rather see a price increase than not getting the quality or not getting the model at all.