I've been working on an unauthorized implementation of Dresden Codak's Dungeons and Discourse, a fictional role-playing game that combines philosophy and high fantasy. You can find a very error-ridden, but possibly usable, rough draft of it at http://www.raikoth.net/Stuff/ddisplayer.pdf. Yes, obviously this is crazy and I have no life. There is no need to point that out further.
I'd like to try to run a campaign. It would be maybe an hour or two a week on IRC, and subject to my schedule, which is terrible and can include disappearing for months at a time (in particular I probably won't have internet access in August). Still, I would like to at least gauge interest and start some preliminaries now. And if anyone wants to run a campaign IRL at a meetup group or something, I can send them the file with the campaign walkthrough, though I'm not sure how much I would recommend it at this point.
Anyone who's interested in participating please let me know (especially if you have philosophical beliefs wildly different from the standard Less Wrong hive mind, or if you know any interested parties who do, since the game would be dreadfully boring if everyone agreed on everything or for that matter anything). Also, I suppose if people want to record the errors and contradictions and non sequiturs and exploits in the manual you might as well post them here so I can fix them.
Plusses:
As further plusses, lots of creative and thematic mechanics:
Minuses:
On Dialectic: Having debates as an explcit part of the game is nice. Just having them amount to "argue until one of you gives up, with the DM deciding who wins if you can't agree" I'm not so sure about. On the other hand, it means that you'll be spending plenty of time debating things, which is nice. On the other hand, it's going to be hard to constantly come up with new angles into the debates - especially if the players don't have PhDs in philosophy.
Borrowing something like Burning Wheel's Duel of Wits mechanic or some other social combat system might work. (Though in BW, debates are explicitly about persuading an audience, not about finding the truth.) I particularly like BW's approach in that each time somebody takes damage, they have to make some concession to the opponent. That's more interesting than just declaring one participant the winner and another the loser.