I would love DX11, but my instincts tells me that ain't happening. Consider that PC gamers make up only ~15% of the market share for Bethesda's games.... To revisit the game engine, overhaul it, and recreate thousands of assets just to appease such a small demographic when their time and resources are already limited to getting DLC out quickly.... It just seems unlikely.
Well, for one, the game engine wouldn't need any "overhauling", and for two, a lot of those assets are probably already available in some form to the developers. I'm also curious where this 15% figure came from.
That said, I'm skeptical too. The picture the entire rumor is based on doesn't have any real backing or explanation to it. Either way a texture pack is a realistic guess for the "surprise" and TBH the game really needs it. Just look at the textures for some of the game's clothing. It's blatantly obvious some things are just flat out lower res than others for no reason, to the point where it actually looks like they messed something up with the final versions of the archives before release. Look at the difference in texture quality between Steel Armor and Ebony or Hide Armor for a decent example. This kind of mess wasn't present in Oblivion or Fallout 3.
Considering that, not all the game's textures would need to be made "high res" they would just need to bring the lower res ones in line with others, possibly by using whatever ones they intended to pack with the game in the first place. Overall making the idea of a texture pack pretty plausible.
A DLC announcement this early would be very strange, and consoles get that stuff first anyway. Bundling that kind of news together with the CK wouldn't make much sense. PC users don't particularly care about DLC right now before patches and the CK, and console users probably don't care much about the CK.