@ganymede This is what I ultimately went with (in the wee hours of last night when I thinnnnnnk I have the default list in, and now it's just adding piles of weird specialty-type things and tagging them wherever they're relevant). It's 'Convince', but the writeup covers it:
The ability to tell a convincing story and be believed by others. Whether the story or explanation is completely true, partly true, or entirely false doesn't actually matter, though expertise in one of these areas may add to the character's effectiveness in the task.
...then people can basically take additional expertise in things like 'pokerface' or 'lie' or any number of other things that can apply to which direction they're trying to take it to apply when its relevant to what they're trying to achieve. (Expertises are more or less like interdisciplinary specs in WoD, apply where relevant, they can just have more than 1 level invested in them.)
I like the versatility of this in that it lets someone decide they're maybe only so-so at telling a convincing story, but damn, do they have a great pokerface whenever that's relevant (sometimes when trying to convince someone of something, sometimes when actually gambling, when trying to hide emotion, etc.), while someone else may be able to sell any story they like (focusing on the 'Convince' task) but their focus is specifically on that alone.
I'm not good at explaining things just now, but I think that is something I'm going to stick with as one of those 'tailored to this environment' things, though it's not one specific to social systems at all. Namely, it gives people different ways to really customize their characters and make them unique and versatile -- which is easy as pie when you have maybe 8 people around a table, but damn do people start doubling up at record speed on a MU* in ways that can be frustrating. Everybody likes to have something they're especially shiny at, which is totally reasonable and human. It gives people more room to have 'their thing' without nigh complete clones in abundance. I'm not super keen on indulging snowflakeyness, but I don't think it's bonkerstown or overboard for people to like being able to have a niche that the system reflects to some extent. So, in the above example... either of those people -- Ms. Pokerface or Mr. Convince -- would be good at that the same thing in one case, but would diverge from there based on where they chose to invest their points/focus.