Thinking about...

I have few thinks.

1. houdini should emulate css4 element(). For example draw img, canvas or video on painting. Because in isolated worker, should be ability to receive from javascript image data.
2. houdini css painting should usable for: content, background-image, list-style-image.
3. houdini should in some variants have access to concrete element (css3 attr, if browser can). Access to element should be optional.
4. houdini should have custom css animation API, or full animation in JS.
5. houdini painting should have support of WebGL.
6. houdini should have custom selector API through function that gets arguments and collect elements on DOM.
7. houdini should support many browser engines or architectures.
8. (offtop) HTML5 Canvas should have support for extracting animation or video data, such as frames or delays.
9. houdini painting should have support SVG.
10. houdini should have extended high DPI support.
11. houdini should have access to events (animation, hover, etc. ).
12. houdini should present api to pseudo elements. Such as events, access to main element, etc.
13. houdini should connected with main javascript optionally.
    Later I say other list.

Read this if you get free time.