> Key exchange would be easy in real life

We are over a year into a pandemic which involved wide-scale lockdowns. Physical key exchange is a nonstarter for broad adoption.

>We are over a year into a pandemic which involved wide-scale lockdowns. Physical key exchange is a nonstarter for broad adoption.

I think the emphasis is on the -ed in involved. That's a temporary condition which is already resolving in much of the world. You may also be overestimating lockdown compliance among average people.

You can always just have it as a feature for super users.

Yes and no. It's not 'hard' it's just friction that's not present at baseline (when iMessage was designed, and for the most part still today). Sometimes you send messages to someone who you haven't ever met in person, or you met but didn't think to exchange keys at the time. And when Dave drops his phone in the lake and buys a new one, he would have to sheepishly re-meetup with everyone he interacts with.

If iMessage had been designed to require a brokerless key exchange, its security would be superior (though in this case, Apple's interception software trumps everything). But iMessage would appear to be less convenient than alternatives like WhatsApp (brokered key exchange, re-keying).

It could offer both brokered and brokerless key exchange, distinguishing between messages from parties verified through each method by, I dunno, the color of the text bubble.

So key signing parties would resurface? :)