The addition of maps is really awesome. In my applications I've had records, which are kind of like C structs, being passed around to represent state. But if I need to add features the records become very constraining, because adding another key to them invalidates any previously existing records when you do a hot reload. So you have to jump through a bunch of hoops to get the records migrated, or just restart the whole system, which is less than ideal.

With maps this whole class of problems goes away.