I agree that there will always be some instances of key changes, and that you can't make that too scary or else it just drives users away. But it's not all or

I agree that there will always be some instances of key changes, and that you can't make that too scary or else it just drives users away. But it's not all or nothing. Signal could do better at improving their UX to reduce the number of key changes people make in practice. If they did, they could probably make the prompt slightly more scary (but not Keybase-level scary) – but even if they didn't change the prompt, the mere fact that users wouldn't see it as frequently means they'd be more likely to pay attention when they did. In particular, according on other posts in this thread, the backup/restore mechanism that allows transferring a key between devices currently has poor UX, only works on Android, is buggy. Obviously that should be fixed. Once that's done, they should make the app actively prompt you to transfer the key as part of the setup process, using a QR code scanned from either the previous phone or a linked computer. You would still have the option not to do so, and some users would inevitably choose that option (if only out of laziness), but if transferring the key is seamless enough, a decent fraction of users would do it.