I would say no, for a couple of reasons: first of all, tags are mostly supposed to indicate the subject of a question. The point is that people can follow tag X to stay informed of new questions about X, and also that you can easily search for questions about X. Tags aren't supposed to give general meta-information about questions. Admittedly, there are a couple of examples of tags that break this guideline, like homework, but we'd like to avoid coming up with new ones.
The other reason is that I would expect the quality of the site to suffer if we have constraints on what kind of math to use. As Lubos and dmckee and others said in the question you linked to, sometimes it's necessary to use math of a certain level to give a proper explanation of something; for example, any explanation of the Higgs mechanism that doesn't mention gauge covariant derivatives probably isn't doing it justice. And other times, the math gets in the way more than it helps. In many cases, there are answers of both types that can be posted, and I don't think it's a good idea to restrict any of them; in fact, multiple answers to a question at different levels of mathematical sophistication can be much more informative than each of them would be alone.
The other other reason is that if a questioner is looking for a particular kind of mathematical background, they can just say so in the question. Of course, as I was saying in the previous paragraph, we may not be able to follow that recommendation, but the point is that even when we can, there doesn't need to be a tag for it.
The other other other reason is that a lot of people don't use tags they way they're intended anyway ;-) usually because they're new to the site and haven't been around long enough to know our tagging conventions.