I do not think I am a composer, despite having written hundreds of piano pieces, and probably not a pianist or a musician either in any of the normal ways these words are used, so take anything I say with a good pinch of salt.
I have to say that I am inclined to tentatively agree with Matt. On the face of it, a composers' forum seems a constructive idea but in practice what would it do ? Now playing the piano is different because there exists an objective basis to everything - the physical act of playing and how to do it most efficiently. There is real value in people posting details of their practice methods, how they finger double notes and all the rest because readers can try everything for themselves and, every so often, find something which helps them a great deal.
I am not convinced that the creative mental processes of composition and improvisation can be described and assimilated in quite the same way. This is because there is no objective basis to anything. Certainly, one can, indeed must, learn from constant exposure to others' creative ideas, but does the audition room not serve this purpose well enough ? Is not the actual sound musical bedrock ? Does it really require a lot of analysis ? I might like bits of it and dislike bits of it. I might compliment the poster on bits which strike me as outstanding. I might make a mental note of things to try out myself. What I cannot do is assess it on the sort of objective basis required for discussion because my response is completely subjective.
Now those who create music using theories and structures might conceivably talk about composition by making these things their objective basis for discussion. However, I do not use theories and structures at all, and so I lack even this toe-hold into discussion of composition. If composition were defined as the process of imitating musical structures of the past, then yes, a composition forum would have a clear function and contributions could be assessed on a clear basis akin to the fingering of octaves.
But who wants to produce imitations of music of the past ? I don't know about others here but I certainly don't. That's the sort of thing I used to do as a kid when I was learning chords and so on.
I must say, Matt, your picture of the economic and social domination of music is very depressing. Unfortunately your background implies you know what you are talking about and I have to concede its truth, even from the little experience I have of it. All I can say is thank goodness I don't have to be part of it and I can play and create exactly as I please. Of course this is yet another reason why I wouldn't fit in to a composers' forum. Indeed, I have been roundly rebuked in quite pompous fashion on such forums for simply stating the truth about myself.
Why all this sourness about what should surely be an activity of immense personal freedom and joy ? It's a mystery to me. Tell me why and then we'll both know.