I think this is a great idea. As far as the Applescript front ends go, though, I'm not clear on how this would work. You seem to be stuck with the standard toolbox of buttons and backgrounds. For the Objective-C front ends, I think it would work great.
Would it be better to adhere to some of the PC front end schemes so they are interoperable between programs, or do you think they're too far along to agree to a standard?