Separate from my other answer, since that one is a bit of personal tragedy and this one is a more generally-significant issue:
How is MathJax going to be affected?
MathJax doesn’t really work responsively, can’t work responsively, so far as I know. As it is, you can easily define MathJax that extends past the space allotted to questions or answers, awkwardly sliding under the Featured On Meta box and Hot Network Questions. On a fixed design, a conscientious questioner or answerer could avoid that situation by making sure their MathJax doesn’t fill that space.
This comes up a lot on the RPG Stack, where \begin{array}-based tables are sometimes used, and sometimes get rather wide. For an example, this answer quotes a table copied from D&D 3.5e’s System Reference Document, and it just barely fits in the (currently fixed) width available on the desktop version of the site. A different fixed width could be accounted for by adding more lines and wrapping earlier, but MathJax requires doing that manually.
Another example is this answer, which has a table of various options meeting the criteria in question. Notably, a couple of the lines (the “citadel elite” and “prestige bard” entries) have manual line-breaks added to avoid extending into the right-hand navigation. For posterity, it looks like this:
If I remove those line breaks, our result is this:
You can see how Shattered Gates of Slaughtergarde is long enough to extend out into the Related questions section of the website, with the green box indicating 1 accepted answer for “Is it possible for a Cleric to catch up on spell levels not gained because of a prestige class?” covering the lower half of “rgard” in Slaughtergarde.
On the mobile version of that site, these wide tables cause a horizontal scrollbar. Not ideal, but workable. Nothing gets covered or blocked by other content, is the big thing, which does happen currently for over-wide MathJax content on the desktop version.