Update: I've written a more complete set of notes of what I think Indigo is.
Ah, the fun of trying to guess at a new technology before it arrives. It feels like the marketing buzz that surrounds a new film - the intense focus and speculation before an opening night. Steve Maine is trying to figure out what Indigo is, Christian Weyer has a turn as well. Don Box tells us it's a 'state of mind', which makes Steve think its a Zen-thing
I thought Don Box's talk on XML at TechEd 03 was the most revealing where he said the WS-* specifications are being created to support a messaging platform and bus (made me think of TIBCO) for the enterprise. I think that Indigo will continue to support these specifications, perhaps adding wider infrastructure support and an improved object model for developers to access these features. In terms of the object model, I believe that WSE 2.0 TP gives us a good idea of what will be involved. It's interesting two that the pipeline processing model on WSE 2.0 is actually an approach to Aspect Oriented systems, where the Aspects are the pipeline filters.
Just my 2c worth.