Certainly, it would do no harm if the introduction for new users links to the available tools. However, I am afraid that the proposal does not help either.
Users usually do not read the guidelines given in the Tour and Help Center; they read existing questions and answers. Therefore, new posts tend to adapt to the quality of existing posts.
Even if (new as well as well-established) users know the tools, they mostly do not really know what to do with them since they do not know how to properly write quantities, units, and equations. That is why many posts look terrible or are simply wrong. (I suppose, many comprehension problems when using quantity equations are related to this.)
Hence, in order to be useful and effective, any introduction to the available tools would also have to include the relevant contents of the SI Brochure, the ISO 80000 series, and the applicable IUPAC color books. For example, this answer could be a good start.
Therefore, any introduction should not only present the available tools, but also explain what to do with them. Or, better still, the other way round: The introduction should first state the requirements for quantities, units, and equations and then show how these requirements can be fulfilled with the available tools.
mhchem, or don't know that they can make use of it. $\endgroup$