The forum is the only piece of GOG technology that has withstood the test of time. That's why it's still standing, with everything crumbling around it. We all know that it's clumsy and antiquated, but I, for one, would not want GOG to replace it, since, based on repeated past experience, they will likely replace it with something worse, because that is what GOG does best.
And with something which most likely will be much more broken. Even the most annoying bugs of the current forum only have been introduced later when GOG was trying to "fix" things.