Thanks for the request! I agree this would be a great feature to fill in the gaps between releases or if there's ever properties we decide not to have for various compatibility reasons. Unfortunately, making them animatable is very difficult. First, we'd need to know the type (color, pixel, percent, degree, etc.), though this could be a setting on the property. The harder item is that a lot of CSS values are now "multivalue" properties, so it isn't like we can just set a specific value to a specific property - we'd need to know exactly where and how to animate or join values. Take the CSS Filter Effects for example. If you wanted to animate the blur, you'd need to fill this in:
So you can see it isn't just setting a value on a given property name; the blur() function encloses the value. Things get even messier when you consider that you'd want to set the non -webkit prefixed version, and sometimes the standard versions have different syntaxes. And it gets even messier if you want to animate blur and another effect like brightness(), which also belongs to the same property!
They really didn't have programmatic control in mind when they made CSS!
If you do just need to add some CSS that isn't animated, you can do this via adding a
<style> tag in the Head HTML and setting that to a class/id defined on the element via the Identity Inspector.