I contacted Activision support on the 29th November 2012. I wrote in english, they replied in Swedish on the 30th November 2012. (go figure!).
I asked when the Skyfall mission would be released. The response was as follows (original text for those who read swedish, and then my [tweaked] Bing translation:
Tyvärr så har vi inget datum än på när skyfall skall släppas, men så fort vi har ett datum om releasen så kommer vi ut med information.
Unfortunately, we have no date yet on when [the Skyfall mission for PC will be] released, but as soon as we have a date for the release, [we will publish the] information.
So, if you're feeling positive, then the Skyfall mission will come with an update to improve the PC version. If you're feeling negative, then we PC gamers may never get to see the Skyfall mission!
This should not be accepted by players - Activision in *their* advertising and *their* game covers which are still on sale state that the DLC will be present for the PC version. There is no getout for this in the game's EULA either... that you cannot create a case for the PC version of the game on Activision's website is adding insult to injury!