Interesting concept, however the name is silly and this line is a bit baffling:
"I have always wondered why the Allies never worked on anything resembling the “Jagdpanzer” style of vehicles" ...
Huh? Has he never heard of the Su-85 and Su-100? How about Archer?, OK the gun doesn't stick out the front,
but the concept is the same.
The US
did work on fixed casemate, 3" gun Tank-Destroyers, the T24 of 1940/41 and the T40 of early 1942, which was based on the T24. The T40 was standardized as the M9 in April, 1942 and was to enter immediate production, however the Tank Destroyer Board didn't like the vehicle from the speed or mobility standpoints. Production was also a problem as there were only 27 of the Model 1918 3in guns available, thus the project was cancelled.
Also it can be argued that the Christie originated the layout:
Model 1932
Model 1935A
Model 1935B
Model 1936