In my not-so-humble opinion (which is why I'm repeating it again here after mentioning it in a comment):
As long as we are asking for technical upgrades, might as well ask for customisability. That is, ask for the
begingroup extension to be loaded and allow each user to have a customized set of LaTeX macros definable in the profile, which are automatically inserted for every post (see below). This way each user can define his or her own macros and not be tied down to other users' naming conventions.
To be more precise, what I imagine is an editable field in the profile which will contain some sort of "preamble" or "template". Every time a user tries to post a new question or answer, the content of the preamble gets automatically loaded into the text box. (For comments and edits the preamble does not get loaded.) (One other possibility is to add to the text edit toolbar an extra button for loading the preamble text, so that the preamble is only manually loaded on request.)
I see this having several benefits, if used with the
As said before, each user can define his or her own set of macros without interfering with those of the other users'.
The auto/manual loading makes it more convenient (so we don't have to copy-paste or re-type the definitions every time).
The fact that the preamble text is copied into the post, as opposed to otherwise loaded from user profile through some internal magic, means that in the event that the user modifies his macro definitions (or in the event that a user requests account deletions), the previously posted content will not be negatively affected. That is, users don't have to actively worry about backwards compatibility when editing their macro definitions.
begingroup extensions are loaded, I would rather not introduce any global "non-standard"
\newcommands. I would hate to define a new command using a macro name that I know is safe to use, only to find that it broke everyone else's posts on the same page.