Sorcerer King is easily the best fantasy 4X that Stardock has ever done. It has the potential to become its own subset of 4X and be one of the only representatives of a 4X RPG (a term I'm pushing too much, probably, but still super ideal) that exists. You've done some really great things, Cbray, Scott and company.
Because of the quasi-linearity of the end game (currently, there are only two ways to win) and they both involve the Sorcerer King, I'm hoping that with the extra time you've been given to make Sorcerer King a classic (and this could happen), you can flesh out some variability with the end game. This could come in the way of a rotating roster of lieutenants, a rotating skillset or class of the Sorcerer King (and maybe with each class he takes, he'd have the same two lieutenants so you'd know which class he was this game), or even random events that come in the form of the Sorcerer King throwing out global spells that effect your strategies.
I know that Brad has spoken of the 'Dungeon Master' creating something similar, but I've never seen anything like that. If that's still in the plans, AWESOME.
Basically, while I know that your main focus is to polish what you have and to make sure that it's all balanced and working as intended, I think you guys should really consider how to improve replayability a bit. Granted, the minor faction rotation, the various sovereigns, and large list of quests do that a bit, the end game is now where the variability is nearly non-existent. If you can shore that up, I genuinely feel like you'll have made one of the best fantasy 4X games of all time. It's only one of maybe 4 games that I can remember having this much faith in. The other most recent one was Endless Legend and my faith was well placed there.
I think it is here, too. I really do.