My guess: I'm going to assume we are still getting 2 new jobs, both DPS. One casting and one scouting. I think one of the new jobs will be the poster job of the expansion, and that will be the job they reveal on Friday. Why do I think this? Longer speculation below.
The story of FF14 is wonderful. One of the best FF stories ever written. But it is long. Even after cutting back some of the ARR fluff, you're looking at a game that takes hundreds of hours to just get to the level cap. As much as the game really should be about the journey and not the destination, there are some hard truths about the longevity of the game that will need to be addressed. At the end of the road, there needs to be a healthy endgame, which means that there needs to be an adequate rate of replacement for players who eventually leave the game. And the longer it takes to get there, the harder that becomes.
With Endwalker having concluded the story that had been building since 1.0, I think the time for an alternate start is nigh. This is where the two new jobs come in. Like almost all new jobs historically, these ones will start 20 levels below the level cap (i.e. level 80). But unlike other new jobs, these ones are available as starter jobs that players who own the expansion can pick when creating a new character.
When you pick this job, you get an alternate starting story. Your leveling experience is spent learning about the core game mechanics, gaining your actions gradually instead of all at once like older job quests, and concludes with a new level 90 dungeon (trust or duty finder) to get comfortable with group content.
After that, the MSQ bridges with the original. You run into the (former) Scions, they invite you along, and you meet lots of new folks and try to catch up to the story so far. Big twist, however: when you meet up with all of the Scions as a big group for the first time, Derplander is there. He's still the Warrior of Light. You, the alternate start player, are someone else.
What does this mean for veteran players who are the Warrior of Light? Well, you do a bit of intro story, meet up with the Scions, and are joined by someone new. An adventurer with the blessing of the echo who shows a lot of promise. And they aren't the normal Derplander; they are the female Derplander that has not been seen since 1.0. Canonically, she is one of the new jobs and will share the cover with Derplander.
The MSQ from that point on follows the WoL and this new character as sort of co-protagonists like some older JRPGs out there that let you choose which main character you want to start as.
Bonus points if the alternate start takes place on the First before leading you to the Source.