Reading this discussion, I also feel like it might be wise not to allow people to ask for legal advice on such a website, both because of the legal issues (disclaimers are a good idea, but not all countries have the same laws), and also because it usually tends to result in noise and rather low-quality topics – which are not really what SE sites are intended for.
But a reasonable solution might be to require a minimum amount of knowledge and research from the people asking questions, much like what is done on most programming sites through "minimal working examples". Say, moderators would (after due warning) close subjective and non-researched questions amounting to "How do I sue my next door neighbour", but allow questions in the form of:
This statute / decision says [this and that]. Are there other legal texts that go in that direction regarding [this specific matter] in [this jurisdiction]? Are there specific counter-arguments one should look for? What are the precedent on this issue?
Or perhaps interpretative questions like:
This law was just passed / This court ruled that… . What are the possible consequences for [this field]? How wide-ranging could be this change in the law? Can it be interpreted as saying [this]?
This way, people who are not legal professionals can still ask general questions, insofar as they are willing to do a bit of research beforehand, and the format of the questions would be such that the answers can't really be considered "legal advice". If someone wants to know about their case, they would need to ask several general questions regarding each separate issue, and no one would be accountable for the total answer since the sum is usually more than the parts.
Then there would also be questions about learning, legal research, legal citation and legal theory, that an SE website could definitely promote, seeing as it is so difficult to find good places for discussing those issues.
So, what I am really saying is: I think it can only work (i.e. attract professionals and scholars) if we strictly require a certain level of knowledge in the questions and answers. There is no point in having a Q&A site if it cannot attract a few "key" people (or at least some knowledgeable people) to run it day to day.