Making the font size larger than \HUGE in chapter headings with memoir?

You're free to create a new macro called, say, \YUGE (sorry, I couldn't resist!), as

\newcommand\YUGE{\fontsize{48}{60}\selectfont}

or, if you want to go overboard completely, as

\newcommand\YUGE{\fontsize{100}{120}\selectfont}

and then use \YUGE inside the definition of \chaptitlefont.

When you want larger font sizes than usual with memoir you have to use the extrafontsizes option (and scalable, not bitmap, fonts).

\documentclass[extrafontsizes]{memoir}
\begin{document}
  normal {\huge huge} {\Huge Huge} {\HUGE HUGE}
\end{document}

or to get really big fonts, for instance

\documentclass[extrafontsizes,60pt]{memoir}
\begin{document}
  normal 60pt \\ {\HUGE HUGE \\ 132pt}
\end{document}

but you have to be careful about line spacing.

Related