Google says it'll take a few days to roll out the feature to iOS users. You can enable it by choosing "High priority only" from the notifications section of Gmail's settings section. The app will also make you aware of the feature with a popup (below).

Sure, this isn't a complete solution to email alert hell, but it's a good step forward. Now that the industry is finally taking a closer look at information overload and tech addiction -- it's a core goal of the next version of iOS -- hopefully we'll see more ways to help us work smarter.