Support for Forum Software
Support for Invision Power Board and phpBB would be so so helpful.. And maybe vBulletin?
Add my endorsement for having Forum Template features.
If adding forum software support, many people would also want support for bbPress for Wordpress.
You must remember that with each system added that TT can output to, versions will require more time in many instances for the developers. This has been the downfall of other applications creating templates.
Ideally it would be great to get all the current templates in a great state, then work on others when the time is right.
And maybe MyBB?