In terms of battle content, we will most likely never see a change to the Extreme/Savage content Role Dynamic. It's clean cut and allows a vast majority of people to jump into it without having to micro to much.

In terms of battle content, Deep Dungeon is the first taste we got of something that changes the status quo to the game, Diadem had the opportunity to do the same but it fell flat. Eureka from what info we've received seems to be a unique form of battle content that will have it's own lving system(ability system) similar to how POTD weapon/armor works.

Then of course we have the unknown system for the next Deep Dungeon which is said to be different from POTD so we most likely won't just see a carbon copy system with new floors.

I just think the best way to suggest new type of "battle content" is to consider how it could work as it's own unique system away from the establish core system of the game.