I don't know what your mmo experience is but I played WOW at launch on a PvP server and we were drowning in rogues, hunters and paladins in approx equal measure. They made up over half our roster. Rogues were especially loved by PvP'ers. Being able to stalk and ambush other players is an advantage that can be difficult to beat. Especially if you wait until the player is eg. engaged in combat with mobs, low on health etc. So I'd expect Stalkers to be popular at least on WS's PvP servers.