I think could be useful to display on issue view/edit page the "closed on" date after

• "Start date"
• "Due Date"
• "% Done"
• "Estimated time"

This field, named "Closed", is already available in issues list, but is missing on issue view/edit page.

IMHO could be a rather simple modify at theme level.

A further (and more complesx) improvment could be to choose/configure for every project wich fields to display.