There's a lot of scenarios where a specialized addon could simplify testing way beyond what QUnit offers by default. They are usually too specific to be added to QUnit, but bundling them as official supported and maintained addons would provide a lot more value for QUnit in general.

• Integrate/bundle event simulation with QUnit, with optional jQuery plugin 
• Composite suite runner 
• Timer-dependent assertions 
• Better support for state management 
• Helpers for canvas testing 

There are existing addons that deserve better promotation and could be candidates for pulling in:

• SpecIt and Pavlov add BDD-styles wrappers around QUnit 
• Mockjax is for stubbing jQuery's ajax requests 
• Sinon.js can be used with QUnit. Its about mocking (aka stubbing) objects, most useful with the provided mocks for setTimeout