Alisae being a RDM was foreshadowed intentionally (or perhaps unintentionally?) since day 1 of ARR

https://vignette.wikia.nocookie.net/...20130825210445

Alisae wears red pants and a red ribbon in her hair, Alphinaud wears a blue tunic with a blue ribbon in his hair. To this day they both wear the ribbons. I would not be surprised if Alphinaud becomes the main Blue Mage of the scions in 5.0. It makes sense that the twins, being opposite personalities would be twin Blue and Red Mages. They can even assist us in a battle as NPCs and do some Twin Magic shenanigans like Palom/Porom from FF4.