I've now taken seminars in two topics, history and cognitive science.  My history seminars were full of other people, mostly just like me: third and fourth year honours history students.  Some were doing joint honours in political science or psychology, and some were older (we had a pair of retirees in our class, for instance), but we all had more or less the same sort of background.  My cognitive science seminar - listed as phil/psych - was mostly philosophy students, but there were at least three or four psychology students and three or four engineers.  A chunk of the philosophy students and at least a couple of the psych students were also grad students - we had 6 in total, I think evenly split between Masters and PhD.

My experience was that while the cross-disciplined approach seemed to be less "echo chamber"y[0], it also took a bit longer for us to cohere, despite the greater academic experience of those in the class.  (As it was, us old fogeys tended to dominate the conversation anyway.)  For a 10 week seminar, taking four or five weeks for everybody to feel comfortable talking - and it wasn't until the last couple of weeks that we had actual disagreements - is just not fast enough.

I'm not sure how one could kick-start the process.  Obviously, familiarity with one another would help - perhaps UW could look at a series of CogSci seminars.  It doesn't seem to me that there's an attempt made to keep a class of people together, as we had at UNB in my history program.

[0] Google and context will tell you what I mean, if you're not sure.  I'm resisting the obvious Wikipedia link, but here's a Salon article about its alleged effects on the 2004 Howard Dean campaign.