Instead of (or in addition to) the idea of a merc or hireable mob to pull one into the shadows or camouflage, a mob that let's you see people who're hidden or camo.

I think the hiding and camo could be used for PK, and might be an unfair advantage, so if that's there then a way to detect those people ought to balance it.

However, on its own, just the idea of having a merc that could let you know the name (or even just the existence) of someone unseen in the same room (or just area), would be quite handy.

Personally, I'd like to see it allow the vision-impaired Heralds toss the rule breaking assassins and thieves. It appears to be a growing issue among the Heralds.