Forgive me if this is a dupe but I didn't see a thread dedicated to guide ideas.
Something I would really find useful is a compendium of all the epic high level quests in the game. During real vanilla I never got past level 40 so I never got to experience the end game stuff. I would love some walkthroughs and commentary on things like attunement quests etc. Something more friendly and readable than just a wiki article, that reads between the lines a little, offering advice.
I personally don't have that kind of experience or knowledge, especially with regards to attunement quests as I never raided a lot back then! I may be doing something in the future regarding dungeon keys but beyond that it's a blur to me.
However if you're up for making something yourself, or if anyone here is interested in writing any guides at all, then as always I am more than happy to help with formatting and graphics