Current problem
A user may send a message and a moderator has no option but to delete. Sometimes it would be enough to mark it as a spoiler rather than abruptly remove the message.
Proposed change
Permission (role/user) to apply or remove a spoiler to a message. In the same vein as manage messages and a useful, additional moderation permission.
Additional information
Similar but not exact: https://feedback.fluxer.com/p/1214