Suggestion: One-way message box. (Suggestion Box, Submission Box)

I suggest one permission to be added to text channels:

"View Sent Messages"

If a user has the "View Channel" permission ON, "Send Messages" ON, and "View Sent Messages" OFF, then they would be able to type and send messages, but the channel they are sending the messages to is invisible to them.

This could be useful for creating suggestion boxes, document submissions, mod mail, and any other channel where the goal is for a user to be able to submit something without it being seen by the whole server.