I am going to throw a lot of feature requests in the post. I do not expect all, if any of these to make it into future versions. I am simply making suggestions based on personal experience and things I would find useful.
Merge tickets (common reported issue. all customers would receive updates, ability to split, send update to single/multiple as well.) This has been requested by other in the forum as well.
Add the due date as a display field on the tickets view.
Add last ticket activity as a display field on the tickets view.
Add the ability to customize the tickets view (field order, default sort, etc, per user setting.)
Customer registration. Make new customers register for an account, so they can login with username/password in the future (forgot password send reset to email function too!) Add option to allow register with/without capcha, and whether or not to require staff approval before tickets are assignable/submit-able.
LDAP/Active Directory Sync. Assign roles/departments/teams based on group membership. Passwords can be local or linked (admin controlled.)
Customer satisfaction survey on ticket close. Would send to customer when ticket was closed. Configurable for every Nth ticket closed per customer, or for all tickets open, random distribution, every time, etc. Special template for tickets that are reopened, tickets that are joined (this has been asked for by other posters.) Allow a single click opt-out button, and add a never send option on customer profile (see registration/LDAP/AD sync above, special case use, senior executives, etc.)
Track satisfaction level based on survey. Filter/contrast based on Dept, Team, Help Topic, etc. Data should be easily exportable (csv, etc.) Allow tecnical staff to see only stats for themselves/team/dept. (Admin controlled.)
Allow for tech to fill out survey for customer (clearly tag this somehow). Example: tech give customer survey verbally as they are closing out ticket.
Ticket escalation based on ticket inactivity (no updates for N hours) or past/nearing due date.
Appointment scheduling. If the tech determines a physical visit will be required, allow them to send a request (with or without suggested availability) for in-person visit. This allows the customer to set aside time they can be in their office, etc for the tech to visit them. Tech can choose suggested time/date range (can require customer to either deny or agree to a time within the range), and an estimated time needed for visit (N hours.)
Exchange or other groupware task list and calendar syncing. Allow the server to link to tech schedule (and customer if customer registration is used) for suggesting appointment times, add reminders and tasks.
Dedicated Android/Apple app? (A way to get financial contributions to the project?) Mobile app could have a customer sign-off option so if ticket is closed in-person, customer attaches signature to the ticket, agreeing work was completed to their satisfaction.