Think about it: the PCs have made 20th level, scoured the realm of humanoids and bestials, opened the frontier up to trade, established strongholds, invested their treasure, sired a few heirs...what's left but the complex intrigues that fuel George R.R. Martin's epic fantasy series A Song of Ice and Fire? The endgame of D&D and other fantasy games is the beginning of an entirely new game...the game of thrones.
Yes, a couple weeks ago I made the mistake of pulling my own battered copy of Martin's "A Feast For Crows" off the shelf. Now I'm once again helplessly embroiled in Westeros and the Seven Kingdoms that form the basis of the series' tales. I spent today scouring Wikipedia, reading up on Robert's Rebellion and the Targaryen dynasty when I should have been working.
Being back in Westeros once again has got me thinking about how to properly render Martin's A Song of Ice and Fire as an RPG. Earlier this year Green Ronin's iteration of the game came out. I don't have that, but I do have a copy of Guardians of Order's seminal book--the first and sadly last that they were able to publish before folding.
A proper Game of Thrones game, to me, would see the player as characters at the zenith of power in a typical D&D game--commanding a medium-sized household, perhaps, and strong enough to make alliances with similar lords. Then, of course, the machinations of power and intrigue, coupled with the highly volatile nature of Martin's Seven Kingdoms, would present successive scenarios to drive the game forward. In this sort of game, the gamemaster has a lot more to do, since he must be actively pursuing the agendas of many powerful NPCs. Sometimes these agendas will be at odds with the PCs and their burgeoning fiefdoms; other times they'll be allied.
I could see this playing out a lot like Birthright: players make long-terms decisions that might take weeks or months or years to bear fruit. Thus the game must be very farsighted in nature. The GM shouldn't hesitate to say things like, "OK, so that's where we stand. Three months pass, now what do you do?"
Anyway, I'm just starting to think about A Song of Ice and Fire. There's a group that's running an irregular campaign over at my local game store; from reading their Web forum, it sounds like they're playing it similarly to how I'd play it. I'll probably sit in on a session or two and see how it feels. Honestly, I'd rather be a player at this point. Taking the reins as GM of a world like Westeros is a tall order indeed.