I would really like to see a version with a C API capable of being embedded, there's a lot of places where a lightweight HTML renderer would be useful, plus it would make it easier to port to other hobby kernels.
There used to be Gecko as an option here too, but Mozilla decided that it shouldn’t be usable outside of XULRunner and made it effectively unembeddable unless you’re willing to commit to XUL.
The rendering was done into a pixel buffer with inputs being passed though a few relatively simple C++ classes.
I think that a small embedded version would make for a great UI framework with minimal dependencies.