The problem I see is that you have no way of knowing who is readings your posts, who is skimming, and who is skipping over them completely, so you may PM someone who isn't even in your "target audience" (for lack of a better term). Hence why when I asked for feedback on Kai-ro's story, I did it in the OOC so that anyone who may have an opinion could chime in and I wasn't making assumptions about who was reading them. Plus, often times I read something and don't have a strong opinion about it. So I know that, just because I do read a post, doesn't mean that I'm going to have a lot of constructive feedback for it.
I did get a reply by private message, rather than in the OOC post, so there is always that. People could ask for feedback, so that we know who is seeking it, and the replies could be PM'd.
There we go, that certainly seems like a good compromise.