What do you mean by "theming"?
"how does a frame look" vs. "how is drawing implemented" - I call the former theme (e.g. the marker for a tagged window).
I prefer to use antialiased fonts (via xft), i want to alter the "how is drawing implemented" - aspect of the drawing engine, but I don't want to change anything else. I just don't want to touch anything except just some draw_text, get_extents, etc. functions.
With a low-level backend these changes would be stuffed together into a single module (using a rather small interface) thus avoiding code dupplication (de is currently ~2400 lines of code, the changes which would incorporate xft affect around 200 LOC), run-time performance should also be no problem.
--Andreas
