If you would like to request a new font be added to the Font Picker, you can contact Shopify Support and Gurus can file a feature request.
The details shared here apply to the most recent versions of our themes. To keep your theme up to date, check out this helpful document.
All latest theme versions now take advantage of Shopify's partnering with the Monotype font library which gives merchants free access to a wide variety of fonts!
An extensive, standardized list of typeface options is now available, with previews of the typeface visible within the 'Customize' settings editor found under Online Store > Themes > Customize > Theme Settings > Typography.
The best way to ensure you benefit from this wide font selection is to make sure that your theme is up to date!