I have one request. For me it is major and would take Zendesk from 'great' to 'indespensible': The ability to tie tickets to milestones. This would allow a project roadmap to be created, implemeneted, and tracked. A perfect example of this in action can be found at a typical Trac roadmap like this one: http://trac.browsershots.org/roadmap?show=all note: beginning at Milestone: 0.3alpha2, you can see the tickets that are assigned to each milestone.
For my usage of Zendesk, this would be a game-changer.