Wtf do you want? Farming key items for 5 hours then spawn a big monsters? Run to a BC to fight the nm, then rinse and repeat 5 times? Fact is, big nasty monsters at the end of an epic instance is the most epic way to do endgame usually.
WoW could use some diversity, but don't act like FFXI is the epitome of diversity. Dynamis, salvage, and nyzul were pretty much like raid in term of conception.
I see two major issues that could slow down the conception of similar encounter.
First of all, the server lags in FFXI will always be bad. WoW is by far the most responsive mmo I've played, and even then, some mechanics are still annoying to deal with because of the client/server delay. With server located in japan, and a shitty engine, it will be hard to make something that is not frustrating. Remember AV's 2 hour lock? Or the rotating pot in sea? Yeah..thats the kind of thing we would have to deal with.
Secondly, FFXIV has very little interaction with the environment. To implement interesting mechanics, they would need to work their ass off to improve the player/environment interaction considerably. Sadly, from a development standpoint, it requires a lot of ressource, and I'm not sure they have that.
Also, Heigan's dance is pretty old, and there is many encounter that are much more fun to do imo.
One of my favorite fight in this one, and I would kill to see something like this in FFXIV.
The first video show how to deal with the fight and give you a detailed explanation of the mechanics, and the second is hardmode
XI Wiki



