Allow clipping paths to have complex appearances.
Currently, a clipping path can only have one stroke, one fill, no effects, no brushes, no multiple fills/strokes. Well, it can have all the fills, strokes, effects, and other stuff your heart desires, but only one fill and one stroke will be displayed.
I would really like this to change. I use a lot of complex appearance stacks and working around this makes things complicated.
To make this play nicely with existing art, there probably needs to be a switch somewhere for backwards compatibility with existing art that may have a lot of complex appearances on clipping masks.
There also probably needs to be some support for deciding exactly where the masked art goes with regards to multiple fills. Probably by putting the usual "Contents" entry into the Appearance panel for clipping paths.
I don't have a feeling right now on how bitmap effects should alter a clipping path's actual clipping area, but I do feel like vector effects applied to the entire path, whether above all the fills/strokes, or below them, should alter the clipping area.