IN the end there is no solution.
Camping HNM is not casual, it is the anti-casual honestly. So why should it be catered. This is content that SHOULD IGNORE 80% of the mmo population.
Actual HNM camping in my opinion this should not be ballanced for casual. It should be made only for hardcores. (other nm spawns and such can be more casual (force spawn and such)). But the game needs 20-74hr spawns if they want to make the hardcores happy.
The casuals will never like this system, they flocked to WoW because this system was in place in older mmos and it was the focus. But on the flip side most hardcore gamers who still had the time didn't leave to go to WoW or left soon after. WoW only had ~60% mmo market share there is a reason there was not more and do not forget most WoW players started mmos with WoW they were not taken from other games.
The trick to implementing hnms is doing this without screwing over the casuals.
Make all drops from NMS Rare/EX (non-sellable counters RMT). Make all drops from HNMs also drop from instance/force spawn bosses (No competition/forced camping for those who do not want it). Make the spawn times actually random, spawn areas really large, or require non-player controllable scenarios to happen. (counter camping to a large degree)
This is what most hardcore people want. NO ONE myself included really wants old XI again, I think everyone agrees that model is dead. But we want some of the hardcore elements done in a way that does nothing to hurt casuals. It will give us something to do outside the dungeon/raid spam.
You want to make a good mmo. STOP TRYING TO MAKE CONTENT THAT MAKES EVERYONE HAPPY it is impossible. And start adding content for everyone. Add content that casuals hate but hardcores love. Add content that hardcores hate but casuals love. Everyone has something in the mmo they really like there for everyone is happy. Really simple concept...
SE needs to do what they said they would do. Create a theme park. Something with rides for everyone. (or in mmo terms content for every play style)
Some people hate roller coasters, some people love them.
Some people hate bupper cars, some people love them.
Some people like the carnival games, some people just walk by them.
and so on and so on.
That is the thing a true theme park has stuff for everyone it is why you see such a variety of people. Atm mmos are keeping us restricted to the frog pond game and spinning tea cup ride... and wondering why huge groups of people stop coming back to play.