Hi, Dan,
I guess the main one is to simplify the opening of different sets of TDL files. I use ToDoLIst for many things: personal planning, a kind-of-global business plan, and I have one for each software project I am working on, which work as a backlog for the project.
So, to take two very simple examples, I may one day want to open ToDoList with:
\LONG PATH\BusinessGlobal.tdl
\LONG PATH\ProjectA.tdl
\LONG PATH\CompanyWebsite.tdl
Another day, I might want to open it with:
\LONG PATH\Personal.tdl
\LONG PATH\CompanyWebsite.tdl
I can do this by creating two desktop shortcuts, using your commandline option to set multiple files but this involves typing and treble-checking long filepaths in that horrible tiny box you get in Windows when editing the properties of a shortcut.
Using a configuration file for this would still involve two desktop shortcuts but at least each one would have to list just one single file - the path to the TDLC (ToDoListConfig) file.
Once this had been implemented, I imagine it wouldn't be too difficult to have the ability to open a TDLC file inside a running copy of ToDoList and have it process the options in the file. This might be especially useful for many of the other options you offer, since many involve first selecting tasks. In a way, it would be a kind of batch processing facility.
I guess, now I've explained it, it does seem a bit niche, and I imagine you have much more important things to be working on.
Kind wishes ~ Patrick