Ahem... I understand that MathJax is not automatically implemented in all new SE sites, because it burdens the system in various ways. I am currently reading the relevant thread in the History of Science and Mathematics meta. I read that the community members there will have to somehow "prove" that their site needs MathJax in order for questions and answers to be properly written and posted.
I hope that SE won't take same approach for the private Beta of the Economics site, and that it will enable MathJax from the very start: I truly believe that we are going to lose a large portion of the committed users (probably myself included), if they find out that they will have to write Economics questions and answers without the use, or clear rendering of, the symbolic language of mathematics.
UPDATE 1: I just found out that the same issue has been raised two weeks before, here, LaTeX support for economics Stack Exchange and that the post was closed as "off-topic" with the comment
Administrative issues such as this are more suited to the people actually building the site once it is launched
No, they are not. Of course they are "more suited to the people actually building the site" but not "once it is launched". I have launched too many projects in my 25-year professional career to know that issues that can be foreseen are better dealt before they become a problem. And the lack of MathJax functionality from the Economics SE site will be a big problem from second 1 of the private Beta.
Where is the problem to forward this issue to the "people actually building the site" now?
The subject matter "Economics" (and theoretical so), already lives in math.SE as a tag.
The following url
gives the list of questions in math.SE that have this tag. Anyone that will browse this list, questions and answers, should be convinced that MathJax is vital here.