Did you find a way to address the issues presented while keeping #IconFonts?
Basically:
When our friends with #Dyslexia overrides your fonts, font icons turn into black boxes since the font they're using doesn't have support for those Unicode code blocks.
When screenreaders, or voice assistance, reads a site with icon fonts, they read the icon fonts really weird.
For No.2, a site with properly marked aria labels, or marked as hidden for assistive tech, is the solution I can think of.
However, for No.1, I can't think of a way since once the browser forces the user font, all fonts on the site will rely on the user's custom font.
The only other way I can think of is to provide an option to switch the site's font right from the website, so they don't have to override the site's font.
