A server in which PVE was hardcore and if your character died, you die. Of course, there could be minor ways to avoid this as abilities or items for trump cards but largely hardcore server.
The PVP format could be altered slightly because it wouldn’t make much sense for that to be hardcore as well. Maybe scheduled duels could be hardcore with the winner taking all of the persons loot or something.
I believe this type of environment would attract like minded players looking for a serious challenge and have the ability to create unparalleled storylines and dynasties of companies or individuals as the players within the game would treat it very differently than the normal non-penalizing deaths. There could be much popularity here as big streamers could be interested in forming a sort of community within it and people would love to watch the high stress/high reward scenarios play out like high level dungeons on hardcore. There is so much at stake making each decision that much more thought out and meaningful.
Imagine the in-game mourning of high level players that were unable to survive perilous situations and the passing of the torch to the next group(s) up.
The community within the server would be more tight knit than ever, creating such interesting situations.
I am sure there is more that can be done to make it even more interesting but this seems like a really cool idea to start with and people would definitely be interested.