My thoughts are pretty much that this is outside the scope of what Babble is trying to accomplish, and while the functionality seems useful, I’m not sure I’d be interested in integrating it this deeply with Discourse, considering the more touchpoints we have (User card, topic route, notifications, second composer, etc.) the more difficult it becomes to maintain, and the more likely either the mothership or Babble will break stuff going forward.
I can’t speak for the founders, but I’d also reckon that part of the reason that PM functionality isn’t a hugely emphasized part of Discourse is that the product that they’re creating is centered around group discussion, and that back channel communications are often the antithesis of group discussion. I know Loomio doesn’t have a private message function for exactly this reason, and SO doesn’t have a private messaging system either, perhaps for similar idealogical reasons (ie, in a help forum with a strong reputation system, we want all of the things you contribute to be subject to public scrutiny, so you make em better)…
That doesn’t mean that someone couldn’t adapt what Babble’s doing for a different plugin, though 