What was the last time you had any problems with the rendering speed of Webkit in reality? Have you tried the other link in HN, that boots Linux in your browser, with a terminal app, and it still manages to be fast even on my modest system?
Have you looked at some WebGL / Canvas based demos lately? There are now very efficient GPU offloaded rendering APIs that make rendering graphics a breeze, it is no longer a big-overhead thing. If you don't use fancy graphics you're underutilizing your GPU.
[also, TermKit is not just about fancy graphics, but also about user friendlyness/usefullness for some tasks that are not very well handled in terminals otherwise]