You're not sounding too critical at all.
The feedback I keep hearing about Prism and Caliburn "big" are that they are too bulky and complex for people to grasp easily. Caliburn.Micro solves that in a view model-first paradigm.
I've never been a fan of view model first, that's just a personal preference and what has worked for me.
Why does the world need another framework? They don't. They need to learn and understand the patterns that work. My intended audience is people who are using MEF and don't want a framework that can bolt-on MEF, but one that is built with MEF in mind from
the ground up. They are also people who want something easy, lightweight, and fast. This is guidance - I'm not intending it to be something like MVVM Light that people start their projects from - but rather as a learning experience, something small enough
to pull down and play with and understand the patterns and how they work. Because of the license, if you happen to like the way it works, you're then free to grab it "as is" or customize to your heart's content for what you need.
I don't believe frameworks can solve all of the problems and the ones that try to end up failing and creating too much overhead with customization. Something lightweight that addresses the basic common needs - messaging, regions, etc - can serve as a learning
tool and provide insights into how to evolve the framework that specifically addresses what you need.
I hope that helps understand my reasoning. I've never used 100% of another framework - I've always had bits and pieces here and there, so after several projects, decided that taking a "lowest common denominator" approach of what is consistent would
make for good guidance as ALL of my work has used MEF at the core to implement the MVVM pattern.