Lambda the Ultimate

Even though message passing can be thought of as a special case of the generic functions approach, there still seems to be something appealing about grouping procedure implementations and their shared data into logical units as in Smalltalk. I understand that polymorphic dispatch need not be conflated with program modularity / encapsulation, but for some reason it still feels like a good idea to me. I looked around this afternoon for a good discussion of multi-methods vs. message passing and came up empty, so I'm wondering if anyone could point me to one or share their thoughts on the issue.

I am interested in writing a lispy scripting language that integrates with the Apple's Cocoa environment, which is based on Smalltalk and therefore hardcore message-passing based. I would like a seamless connection into that world from this language. But I also want the power of multi-methods. I am imagining a language in which first-class namespaces could be blended with the Smalltalk approach to objects, exposing methods that respond to messages. But within these namespaces multi-methods could be used when they seemed appropriate. Therefore, in the large, the program would be assembled out of modules that resembled Smalltalk objects, but the implementation of methods exposed by these modules could have a lispier style. This is all very vague I know... and there's the obvious question of where multi-methods would belong. Any ideas?