I wish Signal stopped using it. I know you can set a Signal PIN but a lot of the non-techy friends I speak to on Signal probably wouldn't think to, or look through the settings (not that you need to be "techy" to set it, but you know the kind of learned helplessness most people have about tech). At least a prompt for all users to set an account PIN so their account can't just be stolen by anyone with their SIM card.
Another thing is that even if you set a PIN, you'd still have to log into your account relatively regularly so that if you lose access to your number, you wouldn't lose an account. It's logical, given that numbers are reused... But that means that if you want to register without effectively tying your account to your ID (KYC when buying numbers is mandatory in a lot of the world, remember!), you'd have to pay for another phone bill (expensive given that the number's practically doing nothing!) or use a one-time rental... Which guess what, puts your account at constant risk!
They abandoned letting you use the Signal app to send and recieve SMS. You still need to get a code via SMS to activate your Signal account. I believe this is what they are referring to.
Yep, I was referring to that. You can stick someone else's SIM in your phone and log into their signal account if they've not set a Signal PIN. You don't see message history but new messages to that person will go to you.