Hi,
I like these suggestions, especially the idea for 50%-50% 2 column layout using left and right, so I will add LeftAndRightNoCenterCss which will be applied to both side columns in the case where both side columns have content and center is empty. I will also add EmptyCenterCss so it can be hidden in that case and a boolean for HideEmptyCenterIfOnlySidesHaveContent so that the center div can be configured to not render at all in that case.
I will also add settings for LeftOnlyCss and RightOnlyCss, however they will be blank by default and will only be used in the case where it is not blank and when there is content only in one side. I don't want to change behavior of existing skins and I think users should use the center column if they want only 1 column, not left or right and in most cases it should be obvious to the user that they put the content in a side column even if the center is empty.
All of these settings will only be applied to the CmsPage ie Default.aspx so that it will not affect admin or edit pages.
Best,
Joe