Given Android's open source nature and lack of a competitive UI to iOS, why haven't we seen a group of elite usability experts form to create their own platonic ideal of a skin for Android?

While Google does technically accept code patches to Android the process does not appear to be straightforward (http://source.android.com/source/life-of-a-patch.html) I would love to contribute  feedback & design recommendations to Google but I'm baffled as to how to do this. Other software projects that are more community driven like Firefox, Drupal,  and Linux have done a better job of creating some community engagement and openness not only around the source but also in terms of how the product is designed and developed. At this point it appears that the main UI team is driving from within Google.

I think the first thing we need to remember is that Android is not an opensource project the way that Linux is. Android is completely controlled and developed by Google. Once they have a completed version that version is then released with it's source code. So unlike a traditional opensource project you can't simply join the project or submit code. You can take the finalized source and customize it and a number of people have done this, but they are not considered mainstream for the most part as wireless providers tend to only use the version that the handset makers provide. Second, there are in fact a number of alternative launchers or UI replacements. I use the LauncherPro Plus application and love it. ADW and Helix Launcher are also very popular. Additionally, there are the manufacture alternate launchers such as the Sense UI from HTC and MotoBlur from Motorola. Personally I don't think the stock UI is that bad, but I do think there is room for improvement. I would love to see Google buy out LauncherPro and make it the default.

"platonic ideal of a skin" don't mix well with "make $ with ads". Beyond that, I believe that the open source nature of Android is preventing such an ideal. Many experiences have been already made (as noted in others answers). But at some point, there's nothing universal and you will always want to fork this or that. It's much different with Apple: you have to take the iOS ecosystem as it is. You like it or not, but  someone decided for you and you're not supposed to change the system.

I think this is one of the reasons that Google hired Matias Duarte. From what I have seen Gingerbread is a step in the right direction and Honeycomb makes Android that much more attractive from a UI standpoint. The rapid rate of Android iterations makes it difficult for potential skins to keep up. Case in point, Gingerbread was released last month, how long will it take HTC to update Sense? Motorola Blur? Samsung TouchWiz? Froyo has been out over 6 months and Samsung Galaxy S phones are still waiting for Froyo!