Be careful what you wish for. The fact that CSS can be so easily declaratively analyzed is the reason why it can be made reasonably fast at all. CSS has some key restrictions—for instance, that attributes always inherit top-down and never bottom-up—that makes it amenable to parallelism (which is no longer a theoretical concern, as parallel CSS implementations are starting to ship). Adding a full programming language would have the potential to make styling much slower than it already is.