Your article seems to focus on individuals. Consider also organisations.
Transport-level security and authentication of email content is a perfectly valid use-case for an organisation when protection against third-party interference is desired. They don't need to worry about forward secrecy, they just need attachments to be transmitted in a legally-compliant manner.
For example each month HR email me my payslip as an encrypted attachment. I decrypt it and save locally. They just have a batch job that encrypts for each user and sends. They don't have to worry about who uses which IM client. They don't need to care if I self-host or use Gmail, because their ligation is simply to keep the information secure in transit.
You are also too keen to support Signal's use of phone numbers as identifiers. That's a design choice, instead of using client-managed identifiers, and makes it unsuitable for organisational use. Whose phone will we use to send the deposition to the court... and who in the court will have a phone with Signal on it? Email by contrast is universal and integrates well into organisational processes without dependency upon individuals.
Transport-level security and authentication of email content is a perfectly valid use-case for an organisation when protection against third-party interference is desired. They don't need to worry about forward secrecy, they just need attachments to be transmitted in a legally-compliant manner.
For example each month HR email me my payslip as an encrypted attachment. I decrypt it and save locally. They just have a batch job that encrypts for each user and sends. They don't have to worry about who uses which IM client. They don't need to care if I self-host or use Gmail, because their ligation is simply to keep the information secure in transit.
You are also too keen to support Signal's use of phone numbers as identifiers. That's a design choice, instead of using client-managed identifiers, and makes it unsuitable for organisational use. Whose phone will we use to send the deposition to the court... and who in the court will have a phone with Signal on it? Email by contrast is universal and integrates well into organisational processes without dependency upon individuals.