The Pentagon announcement quoted above gives the launch site as being "Sain Ni". Is this a new launch site or is it one which we know under a different name?
The logical next step would be use of a second stage with 4, rather than 2, engines. That configuration has already flown in Iran.
We do not know how heavy a payload this missile carried, but given the increase in range it seems likely that it carried a very light mock warhead. If true, that means it would be incapable of carrying a nuclear warhead to this long distance, since such a warhead would be much heavier.
Aren't major European capitals now also within North Korean Missile range, and not just American ones? I'm assuming their quickest route to hit Europe would be launching over the polar region.
It looks to be the 2 nozzle 80 ton thrust engine, with the 4 engine upper stage. So, yeah, now they have either a small ICBM or a decent IRBM, based on the payload mass.