Here's a question I'd like to answer: is it possible to combine (a) the rewards for skillfully communicating via character play, with (b) the clarity of manipulating stats and dice?
Here's why I'm asking: despite all the risks of "just roleplay it out" and "guess what the GM's thinking", I like getting places in games through character portrayal, as a player or a GM. Dear GM, by all means, challenge me to give your hostile NPC a reason to spill the beans. If I succeed, go me! Dear players, absolutely, dig for what my NPC knows! I'd like to hint at it, and lead you towards it, and give it up if you earn it, and if I can pull that off, it feels awesome!
Rolling well on a Persuasion test is nice too, but in my book, it doesn't really compare. Is that just me? I don't think so. I think the thrill that comes from succeeding through your own skills is pretty universal. The question in RPGs, though, is: how do we craft good skill challenges about make-believe?
Every old-fashioned game-stalling physics debate shows the difficulties of looking to the fiction for what's at stake, what's possible, what would work, and whether any given action portrayed by the player and undertaken by the character is "good enough". It's no wonder that some games let the dice decide what happens, while others advise groups to figure it out for themselves. We probably all know some games with good social conflict mechanics, where we make fun choices about what to attempt, and we get to portray the attempt and outcome all we like, so it's easy to not mind that it's the dice and the character stats, not us, determining the attempt's level of success.
Easy, that is, until you get into the habit of doing it the other way. Of earning it. In two and a half years of playing Delve with my buddies, the pure roleplay of the social conflicts was one of the highlights, and I miss it. The four of us aren't necessarily actors you'd pay to see on a stage, but we're all capable of getting "inside" the fiction and acting in character. So when I have a shady, useful, dangerous, deceitful wizard approach the player characters, and they hint and haggle and probe, it's quite a rush. Will I entice them to give this guy more access to their knowledge and power? Will they spot my "tells" of his angle, and concoct some offer I don't think he'd refuse?
In Delve, the principle is that GM and players work together insofar as they can while staying true to the fiction (as established through play or GM prep). So I know that my shady wizard is smart and suspicious, and I can't violate that by having him fall for some transparent line from the players. Beyond that, though, I'm doing what I can to get the player characters something they'll value from this interaction. The players are doing the same. I drop clues, they seize on them and try various conversational tactics. I act out some smirking and avoiding eye contact; they act out some indignation and menace. And usually, at some point, they'll hit upon something this NPC wizard can't resist. Sometimes it's something I had in mind from the beginning, and I'll congratulate them, "Yup, nice, you figured it out." More often, it's something I'd never thought of, and I'll congratulate them differently, "Whoa! Really? Brilliant!"
There are other times when the NPC will totally sucker the player characters, and I'll get to enjoy leading them into more danger. Or hostilities will arise and the NPC will depart in fear or with threats. Sometimes the players simply fail at the challenge; other times, they decide something else is more important than winning. This can end up in regret ("We never should have trusted that wizard! What were we thinking?"), or the exact opposite ("I'm glad we didn't ally with that with that shady bastard, regardless of what he could have given us!"). Sometimes it felt like losing, and my buddies weren't thrilled about losing, but once the pattern was established, and they won more than they lost, and felt like they'd earned their fates, we had some great times.
I could go on for pages about the techniques I used as GM to make it clear to the players that this wasn't some lame "read Dave's mind" guessing game that might be a waste of time, but in the end I am hesitant to recommend that direction. It isn't quick, and perhaps I'm using GM skills that may be non-universal and hard to acquire quickly. What I'd rather do is hand Delve over to other groups with some rules that make all this clear. Something where a player can try an approach, and spot whether it's working, and why, and thus learn through practice.
But is that possible? Can any rule give a player kudos for correctly reading the GM's portrayal of an NPC? Can any rule tell a player why their demonstration of anger wasn't enough to make this NPC cave in?