Checkout the AdvAgg module [1] it does async font loading. It was used to speedup the frontend of drupal.org and the results are fairly remarkable [2]. Also if you looking for more ways to speed up drupal checkout my DIY Drupal 7 Performance [3] presentation.

[1] https://www.drupal.org/project/advagg/

[2] https://www.drupal.org/node/2493801

[3] https://docs.google.com/presentation/d/1Vaad5ToVU1lc7zWdN3qN...