A separate channel has been proposed before and my answer, as usual, is an emphatic no. A problem doesn't get solved by simply making a new room; it seems far more logical to just address the problems with the current room and go from there. We occasionally get bad wiki articles and go through all sorts of trouble trying to fix it - why not just make a new wiki for only serious and good articles? Because now you've got two wikis to moderate, with different schools of thought governing each one and no guarantee that you've actually solved anything to begin with.
The complaint about Site19 has been the same for the past several years, and it is not going to change no matter what we do. A new room will become the new Site19 eventually, with all of its same problems. You'll only delay the inevitable.
It's mightily easy to say "yes, of course I'd like to have more SCP related discussion in the chat!" I would like this as well, but there is only so much you can do to improve it. Short of strictly enforcing some sort of draconian 'no nonsense' set of rules to force people to only discuss what you want them to, there isn't a whole lot beyond what's already been done. If you want me to start kicking and banning people who are talking about unrelated things, I can do that. But you won't like it, and neither will I. That sort of makes me wonder how exactly a critique only channel would be moderated, but I digress.
Is there something I am missing? I have always been open with people about how things are done and why, and if anyone has a suggestion for something reasonable that hasn't been tried before, I would be more than happy to listen. So I ask again, what exactly do you want to do?