As all of this messages are off chain, there could be a possibility of user withdrawing from the visibility stake, to mitigate that, the withdraws would be not possible or require a long time span from its completion, like 7 days, and locked if someone tries to slash, and restart after judgment is finalized.
Remembering that challenging an non-misbehave message should cause the challenger to lose it’s visibility stake, and that this is a social decision taken by an SNT based Democracy, where the loosers of decision don’t get any reward, but winners get a reward, or by an external DAO (such as https://kleros.io/ ).
Status could do this internally as an sub topic of Topic Democracy, a DAO system Status is developing, which is an abstract democracy model providing delegation and voting, that could be extended in a sub topic to have different types of rules for different types of actions of controlled (by this DAO). A discuss about Topic Democracy is being created
This contract could do the locking and allow slashing by a controller (arbitrer/democracy), it can be used as one per public room, or all public rooms use the same contract and value.