How much power could it hold at HF and also uhf/vhf
frequencies? Assuming a modern day high quality N connector??

The other thing i pondered is that it seems the don't make
Pl259/so239 connectors for hardline, so what do guys use typically for
higher power DIN?

Good to Gigs at 5kw. I recall a test of Pl259/SO239 connection vs. N found
the PL259/SO239 to fail from overheating due to the internal mismatch with
as little as 500 watts at UHF frequencies.

I don't recall the Maximum at HF, but High SWR is a consideration. Best to
use open wire feeders in that case.

N is a 50 ohm connector, but the PL259/2O239 is a stepped transistion and
isn't even specified for impedance.