V3 core is extremely old fashioned and everytime more stuff gets added to Chevereto, harder to keep the thing in control. There's no real API, there's no controllers, there's no plugins. No hooks, neither centralized error handling. There's no dev tools, no advanced routing, no return standar, neither JS XHR and so on and on.
V4 real improvement is not more features but a complete new way to present and work with the application framework. The framework is still not ready, I'm close to release but I need more time. This is the foundation for the next 5+ years so I have to take it seriously.
For now, I will try to keep V3 additions to the minimum because I don't want to get the double work of having to refactor these additions into V4. If you want to add your own stuff go ahead, but please beware of the refactor needed for V4.