I have no idea what emergent architecture is in the agile context, but the idea of emergence is fascinating to me, and has been ever since I read "Emergence: The Connected Lives of Ants, Brains, Cities, and Software" by Steven Johnson.
We see the idea of emergent design everywhere in nature and society. I'm not suggesting everything can be built and designed "emergently", but certainly some things can be. See the book (and concept of) "the cathedral and the bazaar". The idea of something useful coming into existence without central planning is an enticing one, and so I can see the draw.