After giving it some serious thought, I think I've figured out how to make a fully customized programming language and compiler in GM6.1 Registered.
What you do is create either 1) your own text field, or 2) a list of functions and variables, kind of like Swish Max. Each of the functions can refer to a piece of GML, which refers to an outside DLL. Once you compile the source code for your program or whatever, and convert it into an executable, you can copy all of the DLLs used in production and bundle them with your application. As far as your application knows, it's a saved game refering to some DLLs.
Just a thought, and a potential find. I'll experiment with it later on and report back.