I'm just wondering why this site isn't called "meta" like the others; it seems kind of odd. Of course, area51 itself is pretty odd, so maybe that's not really so odd; but still...
Well... meta's are usually sites to discuss the culture, technology and rules of the site itself.
Area51 is not in quite the same boat, since the 'proposal' mechanism doesn't exist on a normal site. In some ways, of course, discuss.area51 is the real area51 stack-exchange site, with the proposal feature bolted onto the side.
Area51 is special, and doesn't map perfectly to the normal StackExchange system.
The Meta Cooking site is for discussion about the Cooking Stack Exchange. Following that premise, we didn't want to leave the mistaken impression that "Meta Area 51" would be for discussion about Area 51. It's a different animal.
We wanted a site to discuss actual proposals. Hosting the meta discussions (about Area 51 itself) is largely secondary to the purpose of this site. We didn't want to obfuscate the core purpose… to discuss the proposals.
That's why we opted for the new term, "Discussion Zone."