I'm jumping in here feeling a little less knowledgable in the whole Chapters thing than most. I've only attended one Toronto Chapter meeting in the past 2 years, although I think there haven't been any lately. I also attended the roadtrip this past June.
So the suggestion I'm about to make pertains more to the Toronto Chapter, and others like it (and not so much for the thriving Chapters). And I apologize ahead of time if these chapters have already tried something like this.

What if we started out with an every-2nd-month schedule of gatherings. And every gathering only featured 3 or 4 artists who had a 2 hour period to showcase their old songs, new songs, half-written songs, etc. Artists could rotate one song at a time (acoustically), taking turns for the 2 hour period, with a social break somewhere in the middle, or at the end. The motivation to show up at another artist's showcase would be that you'd want those same people to show up to yours. The artist's rotating their performances would cure the problem of artists leaving after their set.
And similar to the way that we sign up for the Road Trip, members would have to email the co-ordinator to sign up for the month that they're interested in.
In the Fall/Winter leading up to the new year, they would begin signing up for the next year. If all 6 months fill up quickly, then new showcases could be added.
Depending on the number of people showing up, the venue could be a small cafe, or even someone's house. Very casual and supportive though. Non- JPFers and friends of the performers could also be invited to round out the audience.
Again, I apologize if this has already been tried and tested. I'm just thinking out loud here.