It would be nice, if nothing else, if you could run one or more Mp3tag Actions from the command-line. That would be simple, but potentially very powerful.
Seems like a waste of time and energy to interactively open Mp3tag just to perform an Action. This is probably what I do 90% of the time that I use Mp3tag - open the program, select all the files in the directory, apply an Action, close the program.
It's certainly very nice that a clean, well-designed interactive interface is there, but for many tasks it's unnecessary.