What I have seen on the lists is the equation of "tester" and "user," although in reality this is not the same. Of course people need to try it out, find bugs, etc. But there is also metrics-style testing, which can be purely performance measures, bug counts, memory consumption, footprint, clicks-per-operation, DTP-style testing, etc..... This can be some very arcane conversation. It is possible for a person to do this, and not be an Inkscape user at all.
The Venn diagrams overlap, but they are not one-to-one. If we keep these communities together in order to grow the synchronicity, then the members must be ready to participate in the conversation. We have had such good luck so far with our two lists because all of the developers are users.
Actually, I would think there would be more incentive to spin off something like "inkscape-packagers", as the issues dealing with architectures and distributions can be totally foreign to anyone else.
Bob