People who play hardcore for extended periods seem to universally enjoy the adrenaline rush and consequences. To promote long term play on a permanent hardcore server, perhaps something like the following would work:
1) Add special token drops to each level cap raid. An elite or higher completion drops one token for each surviving character.
2) Disable raid timer bypasses on the permanent hardcore server.
3) Add a vendor who will exchange 25 tokens from a specific raid for a cosmetic item. One such cosmetic item exists per raid.
4) Turn off 'reincarnation'.
5) Cap Reaper Points at 40.
This environment would create an end game raid community on the permanent hardcore server. Raid capable characters would suffer regular attrition, requiring constant replenishment. Completing a raid on elite without dying should challenge and thrill players who seek an adrenaline rush.
Obviously, many possible solutions exist to the 'reason to keep playing' problem. I offer this one only as an example.
The hardcore rebels should discuss these matters and find solutions for themselves.