I recently a converted a nice Film Noir style investigation to GUMSHOE. It seems to me that GUMSHOE is a natural choice for any investigative game and indeed it does seem to have fallen into place very nicely. I'm looking forward to seeing how it plays.
Investigative fiction is of course extremely popular: police procedurals, Noir, Agatha Christie style whodunnits, medical procedurals, crime, thrillers etc. Yet published GUMSHOE games tend to focus on investigative genres with a fantastical or sci-fi element. I happen to enjoy those, but I think that a broader GUMSHOE game based on these genres might be of interest to people who enjoy role-playing and investigation, but who are turned off by 'monsters' and the like (my wife, for example).
A single book could contain several genre variations eg. 'Noir/Detective', 'Murder Mystery', 'Suspense' / 'Thriller' etc. It might also be fun to explore psychological stuff along the lines of Hitchcock or even David Lynch. Does anyone else think this has legs?
The following discussion, about creating a bridge between 'Murder Mystery' gaming and Role-Playing, is also relevant: