We have designed one such Navigation. It is a jsp but in true sense loosely coupled. Every new site that is coming up, we just drop a Navigation JSP on the backend and no matter, how the library is structured[it is totally up to the authors and content managers], we generate such xml structure as shown above in the image and throw that onto the portal page for consumption. We have built this as part of wcm site framework.
I'd very much like to see stuff around this topic in the future. However, over the years, we've seen more or less successfull attempts. Why? Because Notes design has soo many possibilities and are inherently quite complex in it's structure. But, that doesn't mean that we lay down the challenge!!
Mika, do you realise how big the Websphere portfolio of products is? Whilst Domino may benefit from being merged with some elements of Websphere, there will never be a total crossover.
What I'm after is the realisation that Rich Clients beat web interfaces for many user-input-intensive tasks, and authoring of web content fits into this category. Therefore Expeditor/Notes8 may give a way forward in that area.