i'd love to see achievements like "past 100days played" or "killed 1 milion mobs", or "spent 20days afk in game" or even "character's 1/2/3/4/5 year anniversary", "Hearthed 1000 times", "bought 1milion food/drinks" - obviously all those should be cumulated since wow started, not just wotlk
stupid things really, that don't mean much, but that accumulate.
or some achievements like "did 15K dmg in 2 seconds or less" "Healed 20k in 2 seconds or less" "Dodged/parried/blocked 15 attacks in a row, for a mob wielding experience", "critted 10 times in a row"
The list is pretty much infinite, and they can add new achievements in every patch now.