In addition to the messenger itself:

What could help would be that those of us paying for Proton could gift Proton Messenger to friends & family, or have a certain number connected to our accounts.

I see the need for messenger, it’s just as important as email. But it relies on the other person also getting the messenger app. Being able to gift or share the membership could be a way of bringing people onboard who don’t want to pay for services.

I myself would be happy to pay for my closest family and friends to have a messenger app to give myself peace of mind!