I'll repeat what I said in my first blog:
We are being very intentional in restricting what can be changed with regards to our functionality and UI. None of this is by accident or an unintended consequence. We are providing tools to create features that side alongside our functionality, and less opportunities to replace our functionality.
We will have a better suite of development tools to enable this.
The third party developers are very important to us, but most customers choose to not use add-ons or modifications. Based on statistics we collect, the most popular plug-in on the marketplace has less than 250 current installations, and the most popular application has less than 600 installations.