As many before have said: The most important thing is that YOU do something you are happy with and spread your creative wings. I have mentioned it before, but I will chip in $1000 for a Kickstarter the first day, no matter what the game is about and how it is played. As long as Chris is head writer and you have your long time PC fans in focus.
That said, I wouldn't be sad if this hypothetical game has lots of dialogue and the choice & consequences you do so well. Deep and difficult strategy if combat is present is nice. Isometric + turn based is usually best for this, but the classic Freedom Force shows that turn-based isn't a must and I really think too few games like it has been made on the PC.
If you want to maximize pledge income, I think you should do what Order of the Stick is doing - adding new milestone goals so that pledging becomes a game in itself. Though with the "entitled gamer" culture being what it is, I suspect great adoration could turn to great anger when some people realize they won't get exactly the game they have imagined. I think managing public relations will be a challenge....
Adding a variety of small games in completely wild settings as subgoal rewards would be cool. Something like the small creative games Double Fine did to get their creative juices flowing again after almost being killed by Brutal Legend flopping.
Ok, the realistic stuff over and done with, time to fantisize:
Some dream settings I have always wanted to see turned into games (but if licence costs would mean less game - screw it, make your own IP):
Anything China Mieville (though it is rumored he only has contempt for games).
The Gentlemen Bastard world by Scott Lynch, rising in the ranks of a thieves guild from being abandoned there as an orphan.
An occult detective story with secret magic warfare and people making disturbing pacts with dark forces set in Victorian London or the court of Louis XIV of France.
A vivid bustling Constantinople of the Ottoman Empire with scheming eunuchs, Janissiaries and princesses of the Purple chamber...
You cooperating with White Wolf to do a single player Werewolf: The awakening game (Werewolf is the only setting that improved in the second generation I think).
A game where you kill the loathesome bad guy, only it turns out he has vital knowledge, so you have to defy the gods and spring his soul from hell.
A game where instead of someone telling you to attack a place, a full-frontal assault will be suicide and instead you have to carefully infiltrate the location! Spying on the change of the guard, seducing intimidating or bluffing guardmen or servants to get a map of the grounds, not knowing in advance what the magical defences are, etc etc.