I'm planning to implement that XEP in Monal as soon
as reporting messages/
users in channels is somehow covered by the XEP. I had even already started
to implement it, when I realized that the reporting element isn't defined for
my channel moderation usecase at all.
You want moderators to use it to report to the server that the spam
originated from? Or you want participants to use it to report to mods of the
channel (ala "flag this message" buttons).