Since AoC will likely have 80% of it's dungeons as open world dungeons, I came with a concept never seen before: gated dungeons.
I would like to hear everybody's opinion about this, this has never been done as far as I know and I suppose it's 100% my idea.
The system is simple: it's just a door
SCENARIO A:
Let's imagine a dungeon has a big castle gate in it's entrance, inside the dungeon there it has a big lever that can be pulled if you have 2 people pulling it at the same time. Your party pulls the lever and it shuts down the gate and you can run the dungeon in relative safety, but not really safe. First party has 8 people.
A second party arrives at the gate and the gate is shut, they will break in by using tools, or ropes, tools that are available in AoC. They have to work on the gates for a few minutes so can they break in.
A third party arrives and sees the second party breaking in and they start fighting each other, whoever wins this fight will choose between waiting the first party to come out or they will force their entrance.
SCENARIO B:
First party goes in and don't close the gate, they have 8 people, they are confident in their pvp skills, they don't need no door alarm.
Second party arrives with 4 people and see the gate is open and they think it is safe, they go in confidently and get ambushed and killed.
SCENARIO C:
Random guy sneak in the dungeon, he doesn't have enough people to shut the gate, he is a solo assassin.
First party now with 3 people goes in and close the gate, they want to use the gate as a door alarm.
When the party is fighting the boss, sneaky guy shows himself and finishes the party off and hide again.
He will stay in the dungeon until a party manages to open the gate or if he finds an exit, he doesn't have 2 people for using the gate lever.
We don't have to necessarily use gates, could use boulders or elevators like in the Wall from Game of Thrones or mini-bosses or else.

The idea is not safety but wandering between hot and cold and having a proper party in the dungeon instead of just a bunch of randoms running around. The gates could work as a door alarm if you are close to it, or if the entrance has a big bell or a thunderous noise could be emmited, so who is in the dungeon will have the "oh shi" momment.
So at the entrance people would probably have some fat PvP, winners go in and they will have some time to breathe, then another party shows up and break in and the PvP may happen again.
This system would be kind of a mix of instanced dungeon and open world dungeon, it is a blend.