GOG should really fix it, but I suspect they relegated GOG mix to the junkyard of their projects.
Hopefully not. It's a good function which is really used by the community. Do you hear GOG? IT IS USED! ;)P
GOG-mix needs de-bugging and a bit polishment and that's it.
But if you're right, they should bring it, and maybe other things, back out of the junk and then put better such things like "pre-order this, pre-order that" or "in development" there. Just my