I don't see a cadence. Fontana should describe that.
The months between versions so far have been 1.0->2.0: 17 months, 2.0->2.5: 12 months, 2.5->3.0: 20 months. 3.0->4.0 will probably be 60 or so months, ie 4.0 will optimistically be released early next year. An explicit goal of 4.0 is longevity; http://wiki.creativecommons.org/4.0#Goals_and_objectives doesn't say how long, but I hope for 10+ years. Each version has been prompted for a particular set of reasons.