Like a continuation of the civil war questline, you would have to help in choosing a new high king, defend cities from Thalmor, take areas away from the Thalmor, and then the last quest is one large battle against the Thalmor.

It'd be cool for sure but considering how closed lip Beth has been who knows.

nah,i want to assault the thalmor, take the fight to them. Also i don't see how the thalmor could move their troops into skyrim without restarting the great war with the empire

The choice of the new High King isn't going to be left up to the player. Helping Elisif to the throne (it's clearly going to be her - she's the only one left standing after the player's Stormcloak/Imperial rampage) just might be. As for a Thalmor invasion, no - Bethesda has made the Great War out to be something epic. A 7-a-side ramble on the streets of Solitude won't do it justice.

Why against? IF they do a Thalmor conflict DLC, and as much as I dislike the them, I hope they add a choice to possibly join/help them.