Well, you know my vote. :) I say we add it to the UI.
Inkscape pioneering adherence to SVG 2.0 is not really anything new...
however if Chrome and Firefox support it already, it's already well supported imho.
Correct if I'm wrong, but the paint order applies to only three things: Fill, Stroke, and Markers.
The default is Fill frist, stroke second, markers third.
For me, there is only one other order than makes any sense:
Stroke First, Fill Second, markers third.
I can't envision any situation where you wouldn't want markers drawn over the top of the shape, so I recommend just two icons:
The default state:
And the Stroke Under Fill State:
The default can be the same as it's always been if we want to maintain the status quo.
Note the red triangle appears when the "stroke under fill" option is selected. If the user mouses over this the tooltip can read something like:
"Currently only supported by some browsers".
Thoughts?
-C