Folks, I have finally figured it out.
Have a baby.
Since having a baby a week ago, all of a sudden everyone is willing to install a decent messaging app in order to receive pics of the baby.
We explained that we weren't ready for images of our child to end up in the wrong hands via non-private apps. Another thing was telling them that the one single friend who had already got on board with this had already been recieving pics...
It's been a conversation starter for many and I think seeing privacy from the point of view of a newborn has helped our family and friends understand it a bit more easily. Plus they've had to put up with it if they want any photos, so they will see it working firsthand.
So, if you want to have a baby, know that it can be a wonderful opportunity to help loved ones communicate more privately.
It also increases the sum total of love, community and compassion in the world and in your own life but that's a conversation for another community :)
Edit: If anyone has good tips on how to share a little one's journey more privately with those that care about them, please post them in the discussion.
Signal is the only thing I advocate. Everything else has a really high bar for nontechnical people.
Jami and Session are as simple as copying and pasting an ID; no more complex than email in reality. But it is a sign of how deeply set in our ways we are that even that can seem arcane when you first use it. Signal does make it extremely easy/familiar.
I really like both Session and Jami's ability to add contacts by scanning each others qr codes too.
I think as more people start using these apps they will feel more familiar and less daunting. I think that really it's a familiarity thing.