For the suggestion of "start with a checkbox option to begin at Lv1 or Lv60", they might not even be able to introduce a mechanism like that, as the game tends to be quite rigid with that sort of thing.

On the other hand I've previously wondered if they could implement a two-tiered unlock system by having some kind of bare-bones "here's your weapon, come back when you're Lv60" that would let players get into those classes earlier. Though I would expect something more like Lv30 than Lv1.

It would be very dependent on whether the 'unlock class' instruction includes a "set to level X" instruction that could vary, or whether it's programmed as if you've inherently leveled that class to X already.

I think it could also make lore rather awkwardly restricted if they had to allow for that setup within every story.