All of this pseudonym nonsense is just that: Nonsense.
Either you're anonymous or not.
Also, I think some are misinterpreting the point of this. One of the central issues that I want to address with this feature request is giving the ability to elders to contact those below in the secret society without revealing their identity. That way, the leadership of such a society can be held secret even when the grunts may also be secret from each other.
The point is not to hold long anonymous discussions, but that will be somewhat possible. The point is that the elders know the members, but the members shouldn't easily know the elders. The same for the aspirant ranks. You shouldn't know who those higher than you are.
Therefore, simply allow an option to send a letter anonymously in the secret society and make it fully anonymous (no nicknames) to all except the elders. Alternatively, only allow elders to send anonymous letters within the society.
(Aside: Who all gets a message when a new member joins a secret society? Who is their identity revealed to?)