With regards to the WatchKit apps - I'm sure I read they were static resources - essentially a GUI library that can run on the watch. That's subtly different to being able to render any command in a draw stream, say, from CoreAnimation. The former gives a storyboarded GUI from a resource set (sliders, buttons, etc), with static animated images (!), the latter is more flexible and I think would be less resource intensive watch-side (render display commands vs local GUI library)
If you wanted to go super-minimal, you could even probably stream a compressed bitmap to a screen that resolution over a wireless protocol, moving all rendering phone-side.
There's also still the issue of the native watch apps coming in 2015.
"The Watch app resides on the user’s Apple Watch and contains only storyboard and resource files; it does not contain any code. "