I had a chat with @kisielk about this on IRC, and I think the discussion boiled down to:

  1. I'm (we are?) possibly significantly misestimating the number of people who would ever need a dispatcher.
  2. I would like to have something well-tested everyone can use, but that doesn't mean that it would have to be in lib/pq.
  3. Other packages only seem to support the simpler single-channel interface.

Kamil seemed to think that we should at least start with the single-channel interface and only then consider a dispatcher *if* there's really a need for such a contraption.  After some thought I think I agree with him.