I'm looking into porting the theme support from XEmacs into Emacs.
However, looking at the 21.0 source there are also some features that
could be ported the other way, like:
Doc improvements.
Using customize to set local variables
New keyword :set-after (explicit dependencies between options)
new font attributes
Some of the later could perhaps be emulated with wmperry's font.el
package (same way the current font attributes are handled).
If I start working on these, will someone look at it?