I think it's not a new system at all. It seems more like the trailer is just swapping through the jobs Derplander has had so far, starting with the old school archer, and going thru them all in order, and watching as each one is getting defeated.

This is probably to drive the helplessness home, showing that his current abilities and skills just aren't enough, so a new power was needed. Some say the Warrior of Light now needs to be a Warrior of Darkness now, but to me..

I think this will be a Dark Knight expansion.

So we have had Derplander being Archer in 1.0, WAR for ARR, DRG for Heavensward, and a SAM for Stormblood. Now, it's DRKs turn.