Area 51 has the same look & feel as the other SO sites which makes sense since it will be intuitive to its users. I guess that it also has to do with the fact that they use the same underlying platform. But I feel that the definition phase would benefit from some sort of discussion board. What happens now when people want to discuss the scope of a new site is that the comment area at the top turns into a discussion board (but without the features that you would expect from a discussion board). You also get discussions of the scope spread out as comments to specific questions, making it hard to follow.
I realize that it's very important that Stack Overflow and the other Q&A sites don't get confused with discussion boards, but Area 51 is not a Q&A site.