I would like to suggest a new metric that would show the % of mobile visits of all visits.
Just like everybody else, we have a growing number of mobile visits and we are trying to use this data to convince decision makers about what properties (sites) to make responsive on mobile devices. We are currently doing this in Excel, however, if this metrics would be available as a calculated or stock metric we could add it to our dashboards and our team memembers would be able to see the growing % of vision on the fly.
Report: Pages report
Metric: All visits
Compare segment: Mobile visits (Visit where mobile device exists)
Page name All visits (no Segment) Mobile Visits % Mobile Visits