XP loss and XP rez: This isn't as scary as it sounds. I have been dealing with this mechanic for years in other games and it's a great "learn 2 play" incentive. It also creates a greater demand for priest classes in the server wide community.
All mobs are elite: Soloing should present significant risk and consume significant resources. Grouping up should be the preferred method of tackling content.
All dungeons heroic: This might be the most difficult part to balance since heroics are usually max level only. Level limits for epic items should also be adjusted so that people can wear the gear when they acquire it.
No question marks, exclamation points, tool tips on npc's or sparkles for quests: I play for a challenge, let me explore the world, let me find the quest objectives on my own, require me to read and comprehend the quest text if I am going to have a chance to complete it. These visual conveniences destroy immersion and exploration.
Must be PvP: To keep the challenge compelling it must be a pvp server. With difficult content that requires players to group in order to complete leveling quest content the opportunity for group vs. group world pvp will be very real. This will also add an extra level of danger to soloing, you may be questing alone, but your enemies may not.
Quest sharing: Quest chains should be shareable at all points, but the reward at the end should only be awarded at the completion of all quests in the chain. The current system is too linear and doesn't reward people for grouping up, it actually discourages it to a degree.
No LFR/LFD: Let us build our own community, the old fashioned, tried and true way.
Let me know what you think I am sure those of you who have completed the toughest WoW content have some input. Please read before flaming.
TLDR: WoW is cool, it would be even cooler if it had a hard mode server for people who like that kinda thing.