In short, when this has come up before, my standard answer is simply
that FS is what it is. And what it is a reasonably fast, almost
entirely complete static implementation of CSS 2.1. I think it's
fairly likely that's what it will remain.
(That said, there are certainly parts of CSS 3 [for example,
selectors] that would be pretty easy to implement and pretty useful so
it's not like there aren't things that *could* be done, but we don't
have the resources currently.)
Pete