LCD filter is a pretty neat option to have for font rendering; I find it improves rendering by reducing color fringing when you use subpixel rendering. Adding it to the kcm would just be a simple matter of writing values into fonts.conf, and having it greyed out when subpixel rendering is off. The values are described here: https://wiki.archlinux.org/index.php/font_configuration#LCD_filter There is a problem that some distros don't support it (e.g. OpenSUSE), but I assume the value would then just do nothing.
*** This bug has been marked as a duplicate of bug 378504 ***