IDK if others have suggested this(I'm sure others did) but a questline I want to see in 5.0 is a "fake WoL"
You encounter throughout the storyline a Hyur in a very poorly made armor who claims he's the real Warrior of Light. The fake keeps bragging about how he accomplished what you did,mispronouncing the names of locations; Primals; characters and dungeons/raids, while saying you're the phony.
After you finish the storyline the WoL encounters the fake near crystals and he explodes saying how he is the real deal and accidentaly becoming a primal.
The trial is very mechanics heavy with the party having to deal with 10 phases, each being an ARR job with their own set of mechanics.
After you defeat him, the fake finally admits his errors and goes to try and become an honest adventurer.
What do you think of this idea? And sorry for errors, I just woke up and English isn't my first language.