Since the browser hands font rendering off to the operating system, however, the most pertinent browser-specific adjustment would be updating the (configurable) defaults (Serif, Sans-serif, etc...) for each supported platform - Georgia instead of Times for a default, for example.
You bundle the top 10 most popular fonts and save about half the traffic: counter is ticking about 20M per minute or 201B per week, top 10 fonts were used 136B times this week, Chrome is about 3/4 of users. Bundling would save (136/201)*(3/4) = about 1/2. However, Google would lose about half of their tracking events so I'm sure they've already thought of this and figured the data is worth more than the traffic expenses.
