I am super excited about this. I love the fun visuals, extensive documentation, transparency and honesty about issues with email clients. I think there is huge potential here and I can't wait to see where they go with it. A huge use case that no one is talking about is transactional emails from your web or mobile app. Now you can have great looking emails that increase engagement that look great on mobile email and look (both in design and the underlying code) much like foundation based rails apps.