Border, Background and Drop Shadow, with Line thickness, color, gap, etc for setting elements inside of layouts. Basically, the ability to change the frame properties for Elements in the layout via arcpy
This would give us further capability in controlling the layout via arcpy. I would want more control of the properties but via arcpy. Currently, this is limited.
arcpy.mapping is easy to use, and I would love to see functionality increased to allow customization of everything - beyond line attributes even. Like legend elements!