I've always wanted to experiment with different ideas and concepts in Subterfuge, but there's nothing that allows me to do that, so a Sandbox seems like a good idea. It also means you'll be able to answer your own questions about how specialists work, etc. Some additional features that could use the Sandbox program would be user-made tactics (to share with everyone else on a "tactics" page), and custom maps for private games (or public games actually...) and which could be useful for various game-modes (I've heard the Devs are working on some new game-modes are they?)

This would be fun!

At the moment I think there are lots of things higher on the priority list, but it would be certainly be a fun thing to have.

I must admit, I do like the idea of a sandbox mode.

Will be great for any new players as well, give them the opportunity to try various things out and actually learn while doing.