Translucent windows--forgot all about that...hey, you can draw under the "toolforms"...but it creeps me out so I'm turning it off again. I guess the idea is not to have folks draw under the toolforms but just be aware of the space, right? Hmm, that must be the reason Sketchbook (and KPT, Bryce, etc.) use annoyingly irregular shapes for UI widgets. (A shadow effect might work, too.)
Hmm, just got a crazy idea trying to think of a real-world parallel to floating toolforms: Maybe you could integrate all the tools in a single "super toolform", (expanding tool options? cycle/swap toolforms by keyboard shortcut?) THEN, get the toolform to follow the brush/pencil around the canvas at a respectful distance. (Some kind of flocking behavior: Attraction to brush--aversion to "wet paint", recently painted pixels.) (This is supposed to be like an artist having a brush in one hand and a palette, brush holder, etc. in the other.) Hmm, probably need a modifier key to get the thing to stay put when you want something off it. It would probably drive your users nuts, but it would keep the tools close at hand, and you could whip it out of the way without clicking-dragging anything. (Hehehe, it's now an inertial palette, with friction (Don't forget the clickable "anchor", and so on and so forth....)
Well, don't mind me--just brainstorming here. Thanks for sharing some "behind-the-scenes footage"--sounds like a fun project, (in addition to lots of work). Of course, we can tell that from the fine app your team has put together.