Add the ability to convert sketch figures into centerlines. Next, add the the ability to convert corresponding dimensions associated with any centerline figure to become a diametrical dimension. Note, when placing a linear dimension between a regular sketch figure and the sketch centerline, the dimension automatically converts to a diametrical dimension. I've included a screenshot of some linear diameter dimensions from the Inventor 2014 sketch work space for reference.
Reference the following conversation for further detail.
http://forums.autodesk.com/t5/Get-Help-with-Fusion-360/Diamter-dimension-for-relvove/td-p/4786779
