You could create a binary with a gui that ST2 could talk to. I have thought about that for a few things...just don't have the time right now.
I have thought it would be cool to do a theme editor this way. Create a gui in python and bundle it as an executable (that bundles everything it needs inside the executable, no need to require a certain version of python) with something like pyinstaller. Send the path to your current open theme in ST2 to the executable . The executable would have a gui for selecting colors etc. and creating new rules. The gui would update the actual theme file giving you a nice local gui editor to change colors, and you could see the changes live in ST2.
So it is possible (but very involved), it just depends what you want to do.