Would anyone be up for that? You could use any guild you're aligned with and you would pull off things like WWII British S.A.S-style raids on Thalmor bases and strongholds with the Companions and espionage with the Thieves Guild.

Would anyone be up for that? I'm not sure what you could do with the College of Winterhold but I know the Dark Brotherhood could do assassination missions. Then again the Dark Brotherhood doesn't have much of an allegiance with any nation or province.

I'm not sure about the Dawnguard or Volkihar Vampire clan but they're from a different DLC so they would probably be left out.

The Blades will have another purpose now - Killin' Thalmor.

The idea is brilliant. An anti-Thalmor add on in which the player works behind the scenes to bring down the Aldmeri threat has much potential to it and I have thought about this kind of storyline myself.

However, I am not a fan of having this hypothetical DLC intertwined with the faction questlines (Companions, College of Winterhold, etcetera).

And maybe you could get secret letters of "approval" from General Tullius or Ulfric Stormcloak if you finished the Civil War questline.

what if you're pro-Thalmor?

Then Bethesda might have a pro-Thalmor quest available.