I have used other overlay products and it sounds like piwik wants to add some functionality heres some ideas…
Create an overlay highlighting the top clicked items(with a bubble)
Define active onsite users (use maybe over last 2 mins)
Define avg engagement time on a page(scrolling up downpage, clicking, commenting, gallery viewing) limit 2mins avg, avaoids when someone leaves a page open and unused)
Compare the metrics Day over day week over week, month over month
Define incoming users as directed by social network, linkage(external or interneal), search engine
Top items given a number in ranking, each bubled link clickable to show trended data in a min graph
Show relative acceleration up or down for a real time analysis for a day on a given page. Maybe limit live data to 24 hr period and then make historical after that.(most practical this way else data retention will explode)
hope this helps. Cheers