I think this is a very good idea. However, I can imagine this could be quite time-consuming from a programmer's point of view. Look for example at revision 2 here. The LaTeX is not completely new according to the highlighting software, there are parts that are not made green, so simply running MathJax over the output of the highlighting software wouldn't be sufficient (see this also).
But, what would be easily possible if I'm not mistaken, is to make a button in the suggested edit review queue to view the new post.
Now, it's only possible to view the rendered output difference or markdown difference. Adding a third option to view the rendered output of the post after editing would solve this issue and could also be helpful in other cases, when all the highlighting makes the difference view a little confusing.
Another option, but probably more time-consuming, would be to let the highlighting software see MathJax parts as blocks. Either the block existed before, or it didn't. If it existed in the old post, nothing has to be highlighted. If it didn't exist in the old post, the whole block is assumed new.