Chad pointed me to the Worldwind-dev Email list (I had unsubscribed because not much was happening) thread where it appears that ESRI is interested in collaborating with Worldwind. Patrick Hogan put it very well:

Whoever accomplished this would certainly be deserving of world class notoriety. “This” would be getting the ESRI tools successfully implemented. I believe this is possible through ESRI output to formats that World Wind could pick up. The tighter the integration the better. But it does have ESRI support.

Now there are no details whatsoever as to what this “integration” might be as no one has even though about how it should work. It is easy to put the cart in front of the horse here because generally ESRI culture subscribes to “not invented here”. It will be interesting to see what happens here, but it might take a long time if it happens at all.