Thanks, I think here Pandoc may be a bit overkill as it’s not the full .tex that would have to be transformed but rather only the commands that aren’t yet defined and also the rules would not be standard TEX->HTML & you’d want to keep control over how they are translated. Possibly all this could be done with Pandoc but I’m not entirely sure it would be much easier / faster 
So for instance
\documentclass{article}
\usepackage{xcolor}
\begin{document}
\section{Introduction}
Here is the text of your introduction.
\[
\exp(i\pi)+1 = 0
\]
\subsection{Subsection Heading Here}
Write your subsection text here.
\begin{itemize}
\item first item
\item second item
\end{itemize}
etc \textbf{done} and \textcolor{blue}{hello}.
\end{document}
Would be converted to
\newcommand{\section}[1]{# #1}
\newcommand{\subsection}[1]{## #1}
\newcommand{\textbf}[1]{**!#1**}
\newcommand{\textcolor}[2]{~~~ <font color="#1">#2</font> ~~~}
\section{Introduction}
Here is the text of your introduction.
\[
\exp(i\pi)+1 = 0
\]
\subsection{Subsection Heading Here}
Write your subsection text here.
* first item
* second item
etc \textbf{done} and \textcolor{blue}{hello}.
This is not very hard to do within the current package and I would assume would potentially require more effort from within PanDoc because you’d need to define all the rules anyway.
In any case I think what could be useful is to define “standard latex commands” and have those directly available to the user which would reduce the number of commands you’d end up having to define yourself.