This makes a lot of sense. Intuitively I want to suggest the game should read the list of windowed resolutions from the list of fullscreen resolutions, rather than have them be hardcoded, but I welcome people to point out reasons that would be a bad idea.

It should also be quite easy to add this feature to a jazz2.exe on one's own with a hex editor, while waiting for the next JJ2+ to come around. I'll post instructions later if no one beats me to it.