The number one thing that concerns me about Gutenberg are the things that developers and theme designers can't control, as you mentioned happening at the moment with line-height. Developers and designers should be able to control any option the user could have in Gutenberg. Line-height is one such thing that should definitely be a global setting which, in many cases, shouldn't even be available to the user, for the sake of the design. It's starting to look like half the process of designing a custom site is just going to be hours spent disabling a gazillion blocks and block settings. I'm enjoying the speed of the development and playing with the things that Gutenberg can do, but it's been, and seems as if it's going to continue to be, an absolute nightmare making Gutenberg user friendly to many of my clients who constantly tell me that they're afraid to do anything in it for fear of messing something up. Unless I'm able to hide literally anything they don't need or shouldn't be changing, then it'll be hard for me to get all that excited about new features that override my CSS. I wish I could just export a JSON file or something with all of the registered blocks and their settings that I could just drop into the theme, that would let me turn things on and off easily.