The plan was to base Quanta 4 on the same library KDevelop 4 uses - however development for Quanta itself stalled. See also my blog post from exactly 3 years ago - the situation didn't change much since then.
An update for contributors to Quanta/KDevelop plugins:
Last week in Vienna I moved out all plugins from Quanta into their own independent repository; we now have:
So there is actually a lot happening for Quanta 4 - without even mentioning the kdev-python or kdev-ruby plugins - languages we never had support for in Quanta 3 times.
What's left in quanta? Well - basically an empty skeleton. Quanta is dead. Long live KDevelop.