Well, it is a long winded way of saying "yes, multimethod dispatch is nice". But as he points out, the same thing can be done with double-dispatch (visitor pattern etc.), which is what multimethod has to do anyway, at runtime. But having multimethod is less typing and more concise, which is worth something. I personally can't think of any concise way to add it to Smalltalk.
I did something like that a long time ago. I called it 'Functional Pattern Matching' as I just attended a course about Haskell at that time. In fact it is an implementation of multi-methods:
http://renggli.freezope.org/programming/smalltalk/fpm
The documentation is a bit misleading. All the matching presented can also be done on the arguments. The code itself probably doesn't work with recent images anymore. Try with Squeak 3.6 or 3.7.
Cheers, Lukas