Stealth games are lots of fun in singleplayer. You control one character (Fisher, Snake whoever), kill lots of enemies in a sneaky way and complete missions. The problem about converting this gameplay into a multiplayer scenario is, that there is just one stealth guy and the rest are grunts trying to prevent the stealth guy to complete the objective. By guading it, searching for the agent or whatsoever. For the agent it would probably be lots of fun, like a refreshing SP mission with unpredictable enemy behaviour each time. The question is if it is entertaining for the rest of the players. To me as an action orientated gamer, the idea of running around the level, looking for an invader with a flashlight in dark hallways is not that appealing. Especially not if you get shot out of nowhere and have to wait for half an hour until the agent gets shot or he made his way to the mission goal.
A solution would be to have more agents who need to cooperate to succeed, however the stealth aspect might get lost if you have two big teams attacking/defending and then you have Counter-Strike/Raven Shield/insert "tactical" shooter. Just my thoughts, I'm curious what the others think about it.