it should be only 1 faction. when u create 1 faction u should be decided and devoted XD to play that faction and fight for the glory of your realm. realm pride ftw
when u wanted to play other faction on same server in WAR u had to subscribe another account so I do not see any problem if there would be some account benefits. its WAR - based on rvr (realm vs. realm). no faction restrictions are sweet for pve games. it just do not work for rvr game.
either make it only 1 faction per account or make it restricted for 1day once u login. not logout
and about that spy thing - omg. if u really would like to call it "regular pvp strategy" or something like that - I think irl or whatever when u find out who is the spy u can pretty much kill him. try to imagine lets say medieval castle siege, defenders on the walls, rain of arrows, oil pouring down on the ram, horde of attackers gathered near castle doors hiding behind shields waiting for ram to break the doors. well...not exactly cuz there is one on the ram who decided to be "A Spy", ruining any attempts to break the doors. but its ok, no1 would execute him on the spot or kick his sore ass out of ram because he is wearing attacker uniform....
if u want to spy for destro - do it on destro toon. its regular strategy. u know - u can yell on region chat: "wb of order comming to keep.", "gank grp hiding near kurlov", "enemy ram carrier with 2 guards left order keep." ...
problem with faction is that players are just way too lazy or do not have any realm pride. if that is the case with majority we can pretty much say goodbye and shut down this server right now