USgov., I think they will take any chance given to them to put China, Russia and N.K. in a bad light.
The big question your analysis seems to beg is why #GOP would demand that the movie not be shown. In the scenario where Sony and the USG want to spin this as anti-NK propaganda (certainly this is not out of the USG playbook), why would #GOP play along? I don't understand #GOP's motive in your scenario.
Companies are "brands" for hackers. "I hacked Target. Home Depot was me." etc. Sony is a huge brand. Keep the lulz going, and see how big it can get.
I'm not sure that I personally buy that the evidence is manufactured - that there is motivation enough from the USG to invent that evidence. But this is where there is reached an impasse. There just isn't enough information at this point to really say. Either speculation can be right.
It'll be interesting to watch as this continues.
IMHO, SONY & USgov have more of the first 2 than N.K. and the 3rd can just be made up.