I am looking into using Java to write a game core, then writing the game logic separate either in Java, or using something like Python. This way I open up the ability for any future users to modify the game to their liking, similar to how TES or Torchlight 2 is setup.
However, my main concern is doing this securely. Looking at the Java option, I can't help but feel that this would allow nefarious users from accessing a lot more than would be safe (OS-level stuff, complete access to the user's file system, etc.). So I was hoping that there was some way of making sure that this isn't possible. Ideally I'd like to use something like Python, Lua, or Angelscript to reduce what the mod writer has access to, but I'm not sure how secure even this would be.
So I came here hoping that this is something dealt with on a regular basis, since I know it's a long shot but... I hope to get on Steam at some point, and I can't imagine Workshop support would allow unsafe code.