Design decision wise, it's mostly about simplicity, so no dependency injection, no pre-compiling jsx, no $digest/$apply, no services/factories etc... it's mostly up to you how to structure your app.
It also does not include routing/ajax/REST resource parts and focuses on the interface only. It is designed to be module ecosystem friendly (e.g. Component/Browserify) so you can easily leverage other libraries to fill in the missing pieces.
It became obvious how influenced by Angular it is through the use of its terminology in the source code.
I think it would be a cool idea to take pieces of Angular and try to create a custom framework, although it's probably worth waiting until Angular 2.0 before an effort is made to do that, when Angular becomes more modular.