The correct way to do hardcore vanilla servers:
This will need some sort of appeal system regarding unfair deaths. They will have to sort that out.
Anyway, its all about the leveling so make it all about the leveling. When you hit 60, you have 2 options.
1. Go ahead and play endgame with raids etc. I don't think many really want this option.
2. Players can have their character reset to level 1.
a. The toon gets an official designation of how many times it completed the 1-60 trip. It can be seen on inspection. It also gets a tabard designating how many times it completed the 1-60 journey.
b. They get to keep (5) Five items of their choice from their bags and inventory. Stacks do not count as 1 item. the rest are deleted. All skills are removed and reset.
c. They get to select (1) One new skill, spell or ability from a suite of them. Whichever one is picked becomes a permanent feature of the toon forever. So you can collect them all if you live that long to reset to level 1 a bunch of times.
Ideas for reset skills, spells and abilities:
1. A button to give you Savory Deviate Delight effect instantly.
2. Cut hearth time to 30 minutes.
3. Rest XP recharges at an inn 50% faster.
4. A button to force a quest mob to spawn instantly, tagged by you upon spawning, 1 hour cooldown. (this is probably too much coding for them but we will throw it in there)
5. Boost maximum weapon skill by 5, up to a maximum of 10 for any given skill. Overrides clause (b), so if you added 10 to axes, youd start with that +10 at level 1 or whenever you relearn that weapon skill.
6. Run speed increased by 5%, to a maximum of 10%. So youd need to reset twice and select this option twice to max this.
7. +5 to one resistance, up to a maximum of 50.
and you can add more just not gamebreaking, at least not gamebreaking very easily.
The wrong way to do hardcore servers:
I suspect they will think about creating "seasons" to maximize churn. They will set the season length so that few will ever actually hit 60, thinking that will encourage people to keep playing. It will do the exact opposite and turn everyone off.