[Amps] 200-ohm tank and "un-un" in HF amp design?

[Jim Barber]

Assuming adequate core/wire sizing and airflow, can anyone think of a 
solid reason *not* to design a legal-limit HF amp output tank for 200 
ohms, then use a 4:1 "un-un" transformer to step it down to 50?

I'm curious because doing so would bring the loading cap requirement for 
a 4000-ohm plate impedance down to under 1000pF at 1.8 mHz, which can be 
done with a large air variable alone.

Note: Yes, I know it *has* been done already, but I'm asking for 
opinions as to whether you think it should be.

Thanks and 73,
Jim N7CXI