I haven't seen much discussion about this so I'm going to see what theories people have. The patch trial series over previous expansions has consistently been themed to a particular game:

* HW - Warring Triad (FF6)
* SB - Four Lords (FF Legend)
* ShB - Weapons (FF7)

It seems likely that EW's trials will similarly take inspiration from a single FF title.

I obviously am aware that the Four Fiends exist, but EW is already very laden with IV references and historically we have gotten a more varied spread of past FF content in each expansion. So I am wondering if we can brainstorm what other possible ideas are floating around.