To demonstrate (future) support for visualization plugins, we could show a plugin using a hook to change the tag cloud implementation.
The same would be nice for all the Graphs. This would make it possible to easily change how Graphs are shown in Piwik (OpenFlashCharts2 <-> jqPlot <-> ...).
Marking as wont fix for now (in the idea of 'demonstrating support for visualization plugins') as #1571 is wont fix. Better have any useful visualization in core :)