My guess about absence of a nuvistor power amplifier that it is does not give enough power, there are many other tubes, more suitable for it. And they are probably to hungry for heater current to have any use in battery powered radios.
But I am a radio-amateur, and try to build something from available materials and fave some fun in the process
So I can build an audio amp on nuvistors, and connect it to regenerative receiver on GU-50 power pentode
I have printed out the characteristics and having fun with design.
I don't like the news about microphony. I want also to build a regen on pair of nuvistors
I have nuvistors with long leads to solder them in PCB, but there is a question how to mount them. Can I clean a bit of tube surface and solder it to PCB?