You'll be pleased to know that we've shipped this today!
Simply click on your avatar and head to Personal Settings, then click on the Accessibility tab and click the dropdown to change your font for the content editor.
We've also introduced the ability to change your font to a Dyslexic-friendly typeface. You can read more about this font over at https://opendyslexic.org/
We're always working to improve accessibility across our entire platform, so please reach out and give us feedback on areas we can improve.
As a side-note: this will only change your font for the content editor, so it won't affect other areas of the app.
Thanks, and enjoy!