Hello Mahlon,
Thanks for your suggestion. Unfortunately, the fontsize feature is not available in current version. I will put in a feature request for this.
I can definitely suf=ggest you the work around by going to Tools -> Source code on the HTML editor and use the syntax like this
<font size="X-Large">This is some text!</font> and it should help you in increasing the font size on HTML editor.
-Inder