A distro should be developed like the kernel itself. There should be one community that builds the distro releases and a lot of companies and individuals should drive it into the directions they want.
All the upstream components which make up a distro - Xorg, Glibc et.al. among others are developed in a non-fragmented manner. You don't see two different vendors for Qt, do you ? Building a distro is perhaps the easier part, the actual upstream development which the distros refer to for feature enhancements,bugs etc is where the cake lies. Why else do you think there are virtually hundreds of distros ?