I'm also interested in something like this (reverse Start Date order).
One possibility, without having to change the interface around too much:
Add an option in the account settings for "Include Reverse Sorts".
If checked, then in the Sort drop-down lists, include a "Reverse XYZZY" for each sort field:
Reverse Due Date
Reverse Date Added
Reverse Start Date
Alternatively, you could add a new checkbox next to each Sort box for "Reverse", but that might be a lot more work to change all the user interfaces.