Oooh I love this idea! Thanks for starting the thread!
Here's my take on it, just for fun! Very loose points since I sadly don't have time to sit here and write all day, as much as I'd love to.
The Warrior of Light is at some point in the MSQ where a clear major goal hasn't been defined yet (Let's take the Alzadaal mini arc as an example, but not necessarily where I'd place my idea at all) - you're just out there, you find something that might be cool (a treasure map, a rumor at a local tavern, a relic with an inscription or a magical voice, you name it) so you follow its trail to see where it leads you!
This leads into an early dungeon unlock instead of leaving it for the mid to end of the tie-in patch. My idea actually begins in a X.5 Part 2 instead of the expansion itself as a way to provide some context for new players (you are a veteran adventurer and you're out on a sidequest of sorts) without having to be an extended cutscene where people just stand there awkwardly or do the same 5 recycled animations.
The dungeon ends in a cliffhanger cutscene where you get yourself into an ambush, trap or an NPC you met along the way turns out to be Not The Nicest Guy Around, and you basically either get sucked in by a portal or the good ol' sack on your head and taken somewhere you don't know. All your fancy weapons and things are taken from you and the goal is clear: Find anything that qualifies as a weapon and bring hell to those that stole from you (and get your stuff back, obviously). The new jobs can be quickly picked up in this area or you can stick with your preferred class and your WoL can materialize an aetheric weapon like the Padjali ones, but a new design preferably. These weapons can be unlocked for glam later on, but you have better things to do right now.
So it neatly leads you into areas you don't know at all, the WoL is just as confused as you are and you rely on worldbuilding, NPCs and exploration to find clues on where you might even be. You don't know who to trust so some NPCs could straight up lie to you to throw you for a loop or try to fight you on sight - you will later on find out you are somewhere in one of the recently liberated provinces formally under Garlean rule and they've trapped you with an elaborate plan to use you against Garlemald, Eorzea, both, who knows? They're not going to explain their reasons to you, they're using you!
You're thrust into this difficult situation (you could kill them, but doing so would strike the next biggest war in Etheyris, potentially setting up the next Umbral era if you're not careful - but you'd like to return home in one piece!) where you meet all sorts of people, from commoners to the highest powers, stuck in this complex war of interests. As the WoL, you will use your experience as a veteran adventurer to strike new alliances with those who are willing to hear you out before they kill you and bring your hide to their boss. You will have to prove yourself like you did in ARR but you will be treated with the due hostility/waryness as someone whose reputation is less than stellar from Garlemald's perspective.With this new group of people, you try to make your way to the core of the problem while trying to make contact with anyone who may be out there looking for you (Scions or relevant NPCs for the area), sometimes making progress but sometimes also failing, adding tension. You're strong, but everyone is against you and you have precious little people you can rely on, and you have good reason not to turn all Murder Machine on them, because you will find out clues about the various reasons you're here early into the expansion and slowly find more details as you go (stuff like wanting to use you to gain advantage over other powers such as Eorzea, trying to use you as a weapon against Garlemald if they were to try to lead another conquest into their territory, perhaps they also want your skills to fix problems inside the nation itself, or more personal reasons tied to the ruler of the region)
Also, I just want a nice classic fantasy setting, preferably with a kingdom and court and stuff. We have so many but they're all a thing of the (far) past or basically useless. I want a cool, drama-filled story where you have all the reasons not to use your OP powers, realistic struggles born from the current state of Garlemald (and maybe a chance to redeem the rushed nature of that arc in EW) and just gimme a pretty princess we can all agree must be protected at all costs. Speeeeeeeen but more likeable lmao