> (2) Signal has no system by which you can communicate to "conceptual entities" - i.e. companies.

This has always kind of bugged me with email as compared to physical mail: While with a physical mailbox I can write a letter "to whom it may concern" and throw it in, with email I need to find out if the special, general purpose inbox is info@, contact@, hello@, or whatever other address the company uses, assuming they use the same domain for their email as they do for their website.

On the next level, there is no first-class support for stuff like 'send this message to person X, although it is adressed to organisation Y, where X works.' Basically, acknowledging the legal and organisational reality that while (single) humans might read, process and respond to communication, it is the legal entity that is actually being adressed.