Perhaps instead of worrying about the specific distro being worked on (and distro-specific apps), developers could unite to improve the libraries, services, and interfaces that are used universally.
Gnome and KDE, for example, are the "face" of Linux to the average user. And let's face it... KDE is modern but broken in many ways, and Gnome is stable but behind the times in many ways.
The specific distro being improved is less of a concern if the focus is on bringing stability, visual appeal, and new user interface innovations to the frontend of Linux itself: the GUI interfaces that the average user works with on the system. Working on that aspect would make every distro benefit.