That's been done...in Runebound Vanilla and in Isle of Dread. Frankly, I think Sands endgame is a refreshing break from the standard "beat the big boss" ending. Been there, done that. Sands isn't about the "endgame", its about the whole game. You make progress toward victory as you complete your quests so you always know where you stand. I don't think that this means that the game ends in a whimper either. You still will need to kill at least one Red to get that last quest card, and the Reds are pretty challenging.
This is why Sands is my favorite big-box expansion. I even like playing it moreso than the base game (although the variant challenge decks are great for the base game.)