I sincerely doubt that Twintania's mechanics have anything to do with past FF games, or other games in general. That would be pretty bad design. I also don't think it will have anything to do with a class-specific mechanic, as that would encourage groups not to run Turn 5 without at least <insert class requirements here>. SE already said the current focus on paladin tanks was unintended and they're fixing this in 2.1.

While you can't rule them out entirely, I think any ideas that require explicit knowledge of prior games, or stacking specific classes, or using a specific class at all, can be striked out on account of "common sense for good game design". Nods are okay-- for example, having to kill Odin before he can cast Zantetsuken is a nod to prior games, but it is not something you need to know the prior games to grasp. Ultima Weapon already introduces people to this concept in story mode, so you can figure it out on Odin without looking at past games.