"Rogue" would work better as a term for generally stealthy possibly criminal character, or they could could just not bother categorizing skills anymore which would be my preference.
Socialist would be even better, except it just sounds horrible and even political loaded. By socialist I mean "one that interacts with others". A thief, assasin, rogue, and bard all belong under this umbrella term. Even a hunter if it's heavily based on stealth and barter (to get good prices for the prey). Also people seem to think of a "thief" only in the sense of a "petty thief". Try to think in broader terms (even if gameplay lacks)... Who was Kevin Mitnick? He was a hacker, and lets assume for the sake of argument that he "hacked as a thief". How did he do it? By incredible hacking skills? Nope, by social engineering/manipulation - *social*.
http://en.wikipedia.org/wiki/Social_engineering_(security)
Isn't fraud also theft? Isn't that also based on heavy manipulation of the target? Again, *social* being the key word.
http://en.wikipedia.org/wiki/Fraud
Note the rightmost paragraph and note how many requires "involving with the target".
Hustling and scamming also shines wrt "involving with the target", "being social".
http://en.wikipedia.org/wiki/Confidence_trick
Look at the skills we know are there / have been there: Sneak, Pickpocket, Back Stabbing (Daggerfall), Streetsmart, Speechcraft, Barter/Mercantile etc. They all fits nicely under "Social" if used as an umbrella term hosting also thievery, robbery, and burglary. Thief as a birthsign is ok in my book, but "Stealth" as a category just sounds *off*. then again, "Social" just sounds lame
Lockpicking fits as it is a skill required by many of the "Social" based classes. Alchemy too actually, since we're doing the most basic of alchemy. Not looking for a "where does alchemy go" fight, it's just how I look at things. Lockpicking would fit between The Thief and The Warrior, and Alchemy would fit between The Thief and The Mage. Then again, the categorization into these archclasses doesn't really matter at all anymore.