I think that the main barrier is this: Generic critique questions are, inherently, poll questions.
Leading to all the usual problem with polls and bikeshedding:
- They aren't about solving a problem -- "Wow, that's a really fantastic piece!" is a perfectly valid answer.
- They don't necessarily agree on what the problem is -- "This opening is boring, here's how to fix that" and "This opening doesn't give me enough detail, here's how to fix that" are both valid answers, even if the answers are 100% in contradiction.
- This means answers are impossible to compare. Each is a solution to a different perceived problem.
- A single poster may have multiple suggestions -- does that mean multiple answers? A single answer with five different points? How do I vote if I love two of the suggestions and hate three? If two answers offer the same suggestion, is one of them better than the other if it has another couple of suggestions as well?
- Which answer does OP accept? If each answer is one poster's genuine opinion, how is any one of them "more" correct than any other?
Not only do all these issues undermine Stack Exchanges entire system of voting and visibility -- they also don't provide the (mixed) benefit that poll/bikeshedding questions do on Stack Overflow. On SO, a popular bikeshedding question can attract engagement and activity, from the site and from search traffic. But critique questions are, by nature, extremely localized. They matter to the person writing the piece, but it's hard to find any circumstances under which anybody else will find those responses helpful to something they're dealing with.
- There's almost no reasonable search likely to lead writers to these questions.
- There's almost nothing to differentiate one critique question from another.
- There's no way for a writer to look for subsets of critique questions that are helpful to them right now -- they can go reading everything, but there's no better resolution than that.
So another hypothetical way to help, would be to come up with at least some taxonomy for critique questions. Critique questions asking "is this a good opening" are somewhat more focused than "is this a good snippet"; you could read a bunch to learn about how to open strongly. You could read critiques of romance scenes, SF-nal infodumping; establishing character in family drama; blank verse poetry.
This is hypothetically possible, but I'm very skeptical of it.
- I don't think we've got anywhere near the volume of users and writing we'd need to create a varied body of critique questions.
- Picking a single snippet to be critiqued with little context is incredibly difficult. Many users (and most newbies) will not do it well.
In conclusion, you write:
But, if it is the case questions on specific works are going to always be off limits, it does seem largely at odds with the purpose of the rest of the exchanges.
I disagree. SE is all about Q&A -- that's what it's built around, and that's what it excels at. You can't post code to Stack Overflow asking "Here's some code, is it good? -- you have to narrow yourself to a clear, answerable question.
A Writing.SE for critiques is a very understandable goal, but it's also a very difficult one. Critiques to Writing is like Code Review to Stack Overflow -- asking for general feedback, rather than Q&A. And Code Review is a much more obscure site, more difficult to understand and make use of.
The problem is that writing doesn't lend itself to concrete problems, the way that code does. (Ah, if only Word would tell us, "This story does not compile; excessive POV shifts in Chapter 3"!)
We basically need to make the choice: focus on what concrete problems writing does yield up, or abandon the focus on Q&A.
Neither choice is wrong, but I think there's no lack of writing spaces online that don't have the Q&A focus to begin with. If we're going to be good at anything, it'll be questions that can be framed as Q&A, not the critiques.