It just occurred to me reading this that when I talk about releasing source code I just mean the c++ that comprises the compiler itself and runtime systems (garbage collector, job manager, etc.)
All of the actual C-UP source code is already available as it's embedded in the object files that are part of the download. It can be extracted out into individual files using the 'extract' command as described in the user guide. This includes source for things like the rigid body library, the debugger itself, collections, parallel collections, string formatting, opengl/cl bindings, etc.
You can also just use the debugger to browse source code if you wish (and even view the generated assembly language interleaved with the source.)