Whenever I've seen the topic of email formatting come up on /r/webdev, et al. people cite mobile Gmail as being one of the most problematic clients to design for. Hopefully this will be at least a little bit helpful in that regard.
It's a huge step forward. It effectively means that we will be able to do traditional responsive stuff using media queries but perhaps more importantly, we can stop having to use inline styles everywhere. That means a big reduction in duplicated code and HTML emails that are MUCH easier to maintain. The increase in efficiency will allow email people to focus on creating better content so that emails are more useful to people.