Having given this quite a bit of thought, i offer the following as suggestions for two new track types.
1. Folder track.
The folder track is simply and only, a container, for other tracks. For large projects, with many many tracks, the process of navigation can be challenging when trying to create soundscapes that involve using a track near the top, and one near the bottom of the track list (as an example).
In addition to this, orchestral projects, in a fairly generic sense at least, often involve working in orchestral sections, i.e. Strings, Woodwinds, Brass, Percussion, and so on.
Using these examples, a folder track based use case might be as follows:
A folder track is created, and named "strings".
The user multiple selects the strings tracks he wishes to add to the folder, and drag and drops them onto the folder track, or, the user right clicks the folder track and opens a dialog that lists all the tracks in the project. The user multiple selects tracks from the list, and hits enter to add them to the folder. There are 2 columns in the dialog, one containing all the tracks for the project, and one that lists the current tracks in the folder.
The folder can be "opened" and "closed" with a toggle keybinding, or double click on the folder track header. When the folder is closed, the user only sees a single folder track. When the folder is opened, the tracks within the folder appear. The user can open a folder, work on the tracks, then hide the tracks again.
With this type of folder track, the user can significantly reduce the navigation involved in large project workflow, simply moving from folder to folder, opening and closing as he or she goes.
To remove tracks from the folder, right click on the folder track header, open the dialog, and remove the tracks currently listed for the folder. (select and press delete. This only removes the tracks from the folder column, nothing else.)
2. Text or annotation segment.