Would love to see an author-approved space marked "Concrit etc goes here," however that could be implemented. (Maybe drafts could allow for beta readers? I have no idea how drafts work; I haven't tried one since, heh, very early in AO3's life... it didn't yet accept line breaks.) A "discussion" page like wikis have would be good, but I could see that being a resource hog if it's on all the fics.