Hi there! The short answer is YES, we do have plans on adding in additional fonts.
As far as Google Fonts, I wouldn't be able to speak directly. The fonts that are made available are ones that we are confident will render in the most email clients, so that limits the list a bit.
I don't have a direct time-frame on these improvements, but I do know that our developers are working on a slew of improvements to the editor, and changing out our text-editor tools is going to be a part of that, including adding new font possibilities.
Any timeline on this now? I am rather desperate for additional fonts, including a readable script for headlines, and am considering changing to another email service to get them. Would really hate to do that as I love Emma!