Optimized resource leveling (if there are ticket dependencies)

If I understand correctly, you're saying tickets 3 and 4 are both assigned to user X and since ticket 2 (assigned to user Y) blocks 3, ticket 4 could begin earlier. I don't see that as a resource leveling issue, I see it as a scheduling/prioritizing issue. The rule I'd invoke would be that all other things being equal, a ticket without predecessors should be scheduled before one with. That would accomplish what you want and I'll add that to the list of valuable rules.

My notes at http://trac-hacks.org/wiki/ProjectManagementIdeas#IProjectSchedule are a bit dated but the principle outlined there about complex rules for sequencing tasks still hold. I've implemented this in the existing schedulers which defer sorting decisions to the task sorter (ITaskSorter). There are two implementations in the distribution (SimpleSorter? (sort only by priority) and ProjectSorter? (an attempt to have priority percolate through a ticket hierarchy)). I have plans for a more sophisticated sorter but if you can't wait, you could develop and enable your own ITaskSorter which prioritized tickets without predecessors. Note that the BaseSorter? provides some useful utilities when implementing your own sorter.

Replying to ChrisNelson:

... ticket 4 could begin earlier...

Yes, simply, if they want to plan a milestone, it doesn't make sense to leave X without work when Y is working on 2.