Here's the article I was looking for from Williamson:
http://www.keith-snook.info/wireless...perlatives.pdf
Cathode feedback windings are great, IF you can drive the output stage. In the case of the typical triode or triode strapped pentode/beam power tube, cathode feedback windings just won't work.
In the case of the pentode/beam power tube, this is certainly an approach that deserves more exploration. But again, it comes at a cost, higher driving voltage at the grids and a much more expensive and unusual OPT.