It has been at least 9 years since I used Red Hat. Why is there a CentOS? Wasn't Fedora supposed to be RedHat with all of the proprietary stuff removed?
Fedora is basically the development branch of RHEL. Fedora is cutting edge (sometimes unstable) packages and new technologies to test and work out bugs.
Allow the manufacturer to customize the hell out of it, but write into the license agreement that all functionality must work a vanilla install that is made available OTA. That way a user can go into the update menu and select "update to latest Google version of Android supported by your phone's hardware WARNING: ALL MANUFACTURER CUSTOMIZATION WILL BE LOST". When on vanilla, make the latest manufacturer switchover available. If they did this, how many of us would still be on 2.1 or 2.2? That would be the best of both the worlds.
The only problem I see with this is, who supports the vanilla android install? The carriers, the manufacturer, or the google themselves? Carriers most likely will not want to touch it because it increases their support costs to maintain two or more images and in some cases, ie Moto phones, the junk isn't even theirs to control. The manufacturer would be the most likely source, as they have the vanilla image installed then customize from there. I could see HTC providing default Android builds for their phones without the HTC software installed, but I highly doubt you'd see someone like Motorola doing that. And then you get into fights with the carriers because you can load unauthorized builds on the phones which carriers never really like for you to do. Google most likely wouldn't want to mess with it because now they have to provide images for other manufacturers phone and maintain them.
Make it right before you make it faster.