At the moment, Stealth is on several things, including Elven Boots and the god bonuses granted by Aengus. (According to Graalbible)
This would be a nice feature if it were implemented, allowing players to become almost invisible when they have the stealth attribute. It would also make Aengus a little more worthwhile, since it would passively be on all the time.
An option to switch it on and off might be too much to ask, but I figured I'd suggest it. Might add a fun aspect to the game if it could be temporarily broken by damage / attacking as well.
Shortly after a server restart, a few players turned transparent (which was fixed with a simple reconnect) so this is kind of how it could look if it were in place.
'Stealthed' players are circled in blue because they're kind of hard to see.