I would wanting raiding but different then how most MMOs have it. Believe its been stated already that raid size is 16man.
Then this is my perfect raid hierarchy:
1: A 16 man raid is introduced but its very hard and only the hard core guilds can run them. Time passes.
2: The 16 man raid is downgraded and now a 8 man raid. is possible by the masses though the loot quality is reduced accordingly.
3: The 16 man raid is downgraded again and is now a 4 man group with its loot quality reduced to group level.
4: The 16 man raid is downgraded further to open world contested content that has any of the top difficulties.
That way Raids can still be hard for the hard core, but the mass public will still be able to see the content at some point in the future. I always hated that most raids and dungeons become obsolete once newer content is introduced.