Persistent entry guards will only slightly slow most attackers down, hidden services should not be considered anonymous from any decent attacker. It boils down to this: any attacker can make a hidden service open as many circuits as they want it to. If the attacker has a few nodes on the Tor network, eventually the circuits they force the hidden service to open will be using nodes they own. Entry guards make it so if the hidden service hasn't selected attacker nodes to enter through, that the attacker can only trace it to its entry guards. Which is fine, other than the fact that after the hidden services entry guards are located the attacker can use a pen register / trap and trace order (or tons of other things, but for feds that will be the easiest route to take) to deanonymize the hidden service. Until Tor starts using multiple chained guard nodes for hidden services they shouldn't be considered anonymous for more than about a week or two after they are targeted by any competent attacker.