It sounds likely that the missile this time had no payload. A weapon would increase its mass and reduce its range on this particular test. However, the acceleration of the range of DPRK's weapons is striking, much more than what was expected, and the idea that a nuclear strike on the US from DPRK would be possible by mid 2018 sounds credible.
Any official talk (or even public "trash talk") of “regime change” could trigger a pre-emptive strike from Kim Jong Un, who may be less stabled and less tolerant of indignation than we want to believe. But note that no tests so far have traveled as far as Japan, although they have landed in Japanese-controlled water 50 miles out.
Update: July 30
Max Fisher has a balanced perspective on North Korea's intentions in the New York Times today, link.
Update: July 31
Presumably North Korea could prove it can mount a small nuclear payload with another blast that lands near its own coast after parabolic high altitude route. The reduction in height and distance would give a mathematical idea of how much the payload reduces range. Possibly DPRK could try a test like this from a Chinese-designed submarine in the open Pacific. It's not clear how effectively the US Navy detects foreign submarines approaching its own territory. Some "right-wing" pundits have suggested that a terrorist (with help of a rogue state like North Korea or maybe Iran) could launch a scud from a hijacked commercial ship with a small nuclear weapon to produce an EMP blast. See Michael Maloof's "A Nation Forsaken" reviewed on Books blog April 13, 2013.
Logically, demands from DPRK for the US to withdraw from dedending South Korea (the "hostage") would seem justify a pre-emptive strike, but these might not be made until DPRK had launched a test like described above. Diplomacy with China does not look promising right now, as Trump has previously said "China is not your friend."
Senator Diane Feinstein's remarks on CBS "Face the Nation" July 29 are here. Wall Street Journal is quite blunt about nuclear blackmail of American cities and urges "regime change" from within. That is exactly what could prompt a nuclear strike or EMP attack om us if we're too late. I llike the line "Thanks for letting us know.
And Trump, among all the Carnage in his White House (no one as vomited yet like in Roman Polanski's movie), says, "I'll take care of it," There may be some post-mortem comfort food in the fact that so far North Korea's ICBM's apparently burned up in re-entry, so they may not be advanced as quickly as DIA estimated.