Hi Aere,
having read your document, I now understand what you mean. Ok, you use the currently unused CC 8 in your midi router for different purposes, controlling _expression_. And you fear that if we implement balance properly now, that you can't use your setup anymore, because CC 8 will now have a proper effect (which is unsuitable for your setup).
But if I have read your document correctly, then there is nothing special about CC 8 for you. You simply picked it because it was unused by FluidSynth. Couldn't you just use any other unused CC number? In other words, simply replace CC 8 by CC 102 or any other controller that hasn't got a clearly defined meaning in the MIDI specs?