This is a weird thread. There's a product that does secure messaging with usernames and only requires user/pass. It's called Keybase. If this is the product you want, then go use it. I don't understand why everyone wants Signal to be something it's not. I quite like Signal as they are and this "incident" demonstrates exactly what happens if a carrier gets compromised: nothing. Nothing happens. Signal decides not to trust any phone verifications from the period of compromise and requires affected numbers to reregister. All the important crypto has nothing to do with phone numbers in Signal's domain. And this is exactly why I use Signal. It lets me send secure messages to people using a tried and true UX: text messaging, but with its own secure application layer. It's really difficult to build a useable security product, and Signal has done it successfully.