I looked over the listed suggestions and there might have been one similar to this, but the link is broken so here:

I suggest there be a 4-48 hour server wide event that everyone can go to and fight against a NPC together. Regardless of enemy/ally stance, everyone would show up as allies and fight against the NPC mobs.

For example:
like a foreign invader comes and we have to defend our lands
or a city appears and we have to defend it
or it could be like a temporary adventure hut

About the events duration: If it were a short event, like 4 hours there will be problems getting to the event unless travel could be almost instant like a citadel, also if it were short there would be the problems of people not being able to participate cause they are sleeping or at work. So if it were short the start times would need to be alternated to accompany all players. So I suggest a longer event to insure everyone gets there and it would be easier for administration to hold with less complaining.

I believe this would be a good addition to the game. Something to give us to play together as a whole instead of constantly pitted against one another.

Getting a participation prize would be incentive or something like that.

This could also bring out other activity in the server as other orders will be able to tell whom is in the hut and try something while others sit in the event location.