I would not view imp hoj as a pvp talent, now that it works like a normal interrupt. Its more or less mandatory in a tanking role.
In case interrupts really matter both 60 seconds and 30 seconds are way too long a cooldown for you to count on your Prot Paladin interrupting. We're talking about raid compositions here, so it's extremely realistic that you have a combination of any of the following there: A Mage, Feral Druid, Warrior, Rogue, Shaman or Warlock. Basically, Hammer of Justice functions as a "Okay I have to interrupt and there's really no one else capable of doing an interrupt now" button, and there's something wrong if you need that every 30 seconds in a raid.
I'm not sure why it was brought up in the first place however, as it's easy enough to come up with a spec that doesn't have Kings which still only picks up much more useful talents, a 5/54/12 build for example: Talent Calculator - World of Warcraft
On the other hand, it's still easy enough to tweak this into a build that does take Kings, by either dropping 2 points in Seals of the Pure and dropping Reckoning, or alternatively by dropping Pursuit of Justice and Heart of the Crusader (Or any combination of these two solutions). And yes, before someone asks, I do consider 15% extra movement speed much more valuable than being able to interrupt once every 30 seconds instead of 60 seconds.
Also in regards to "Why pick up Kings if you have Sanctuary?", Sanctuary is only a superior buff choice in most situations for tanks. Pretty much anyone else in your raid would prefer either Wisdom or Might, it's highly unlikely that you will ever pick up the talents for either of those as a Protection Paladin.
Sanctuary is simply problematic to plan in. If you have a Protection Paladin, it's suddenly optimal to plan for three blessings. If you don't, you're fine with two blessings. Pretty much everyone wants Kings and either Might or Wisdom. If you have two Paladins, and one is Ret and the other is Holy, you'd typically have the Ret Paladin buff everyone with Kings, and the Holy Paladin with Might or Wisdom (As the improved version of both of those is easy enough to pick up for any Holy spec). If one of the two is Prot however, you can't work this out as neatly, and it results in both Paladins picking up the full Kings talent to make up for the other Paladins blessing deficiency.