I don't think it makes sense to automatically have a subjective version of every site because different sites have different intrinsic levels of subjectivity.
In fact, the "Chefs" proposal is a perfect example of an unnecessary subjective site. Most of the questions proposed for that site are actually questions that we handle just fine on Cooking.SE. Cooking is an inherently more subjective topic than programming or network administration. It's more subjective than personal finance and statistical analysis. We expect a certain level of "discussion" to go on. We may walk a fine line between discussion and hard Q&A, but we've been walking it for 73 days now and have pretty much figured out where to draw the lines in the sand.
That said, of course it makes sense to create a subjective sister site when all of the following apply:
The primary site is strictly focused on a meaty technical subject;
The site has reached critical mass in terms of membership - the flow of new users and new questions is self-sustaining without any promotion;
A significant contingent of the membership is hell-bent on talking about the fuzzy areas because they want the audience.
So whenever you see this happening - by all means, go and create a discussion proposal - but don't do it too early or without careful consideration, otherwise your proposal will end up like the Chefs proposal did. Just like their "objective" counterparts, a subjective site needs a seed membership to survive, so if we just automatically create the proposals or worse, throw it up as a separate section on every new SE, they'll just turn into permanent tumbleweed gardens. And in the case of inherently more subjective sites like Cooking or Photography, it'll create endless confusion among the new users, especially users new to the entire SE concept (i.e. not from the trilogy).
I would also expect that if and when the discussion sites succeed, they will be linked to the original sites in the form of migration paths. Technically all Stack Exchange sites are "linked", it's just a question of how linked.
Now I have to address some of the rather obnoxious pro-subjective rants that were posted as answers (quite inappropriately, I might add - that was not what this question was about).
Segregating the subjective and objective sites is important for several reasons:
Reputation. Assuming we don't abuse the community wiki "workaround" (which is horrible for countless reasons that I'd prefer not to rehash here), reputation on a subjective/discussion site means something completely different from reputation on a pure Q&A site. It does still have meaning, but for a discussion site it's an indication of how interesting/entertaining you are, while on a pure Q&A site it's an indication of your actual expertise.
Noise. The biggest problem with discussions on a Q&A site is precisely the reason why subjective proposals/sites like Programmers.SE are so successful; they attract a lot of attention. On a Q&A site, that means that they distract attention from non-discussion questions, questions that are actually going to help somebody get work done. This is monumentally bad for the site's health.
Voting. The way voting works on discussions/polls is different from how it works in pure Q&A. In a pure Q&A site, people vote based on the quality and correctness of the answer; in a discussion/poll, people vote based on agreement or disagreement. Question votes are decided on a Q&A site based on the clarity, conciseness, and completeness of the question; on a discussion/poll site, question votes are awarded based chiefly on entertainment value / originality.
Scope. Programmers.SE isn't just for subjective questions, it's also for questions that are related to programming but not actually programming. The most obvious example on Programmers.SE is development processes - there's a lot of "hard facts" on this topic but it just doesn't fit on Stack Overflow. On a pure discussion site, people are naturally freer to stray a little off topic.
It does not make sense to try to concoct clumsy workarounds for maintaining the discussion/poll questions on the hard Q&A sites. All it does is create more work and more confusion for everyone. Please, stop it - we don't need or want blatant discussion questions on Stack Overflow or any of the other SE sites.
Subjective/discussion/poll questions can do fine when segregated; they simply cannot coexist with pure Q&A without doing any damage.