I'm glad you guys are liking the design diaries.
To answer your question about "sneaky types," I'd say that the unfettered is a really good choice. He's got sneak attack and access to a lot of sneaky, infiltration skills. If you wanted a D&D analog, he's sort of a combat-focused rogue. A rogue/duelist kind of guy, sort of. (Really, though, it's difficult to say "AU class X is just like D&D class Y because I strove for the book to NOT be like that.)
The akashic is so open-ended that he would make a great sneaky guy to. On sheer skill use and information gathering, he could "out-thief the D&D rogue" but he is not as good in combat--no sneak attack, for example.
A number of the totem warrior types, like the wolf totem warrior and even the hawk totem warrior, make great sneaky types. There's a sneaky unfettered/hawk totem warrior (multiclass) in my playtest group right now.
One thing that I did was make it easier for more classes (although not every class) to be at least a little sneaky. Because there's often a call for multiple characters to be sneaky. In fact, you could easily design a well-rounded sneaky party if you wanted, which I think is a good thing.
(I did that with other concepts as well. While it's not true of every class, there are more classes with at least some knowledge skills, and more classes with at least a little ability to interact with others, and so on.)