Lumen is a cool project, and definitely a nice boost compared to Laravel, however I think mine and Taylor's definition of micro-framework is a bit different.
I mean it's 10.4MB after pulling in dependencies and only runs that fast with everything useful turned off.
I've been playing with some ideas in a purely experimental fashion and believe it's possible to create a version of CodeIgniter that is every bit as fast as Lumen when it's using only the basics. And since nothing needs to be instantiated until it's actually used, there's no need for a micro-framework version. CI has always been a full-stack framework and that's where I, personally, think it needs to stay.