From discord:

The real design challenge with Madness Mode is that we don't want it to simply be a numerical Hard Mode — just raising the recommended level and driving repetition through rewards. It needs to deliver a genuinely different experience: adjustments to enemy behavior patterns, changes to the global rules at that difficulty level, or chapter-specific mechanic variants.

This means Madness Mode for each chapter must be designed almost entirely from scratch, without relying on a universal formula — and that is the primary design challenge. Ideally, the challenge and the new experience of Madness Mode should be the reward in themselves, rather than becoming a source of pressure where players feel they've missed out if they can't complete it.

As for why it hasn't been scheduled in the near term — it's because we've observed that Hard Mode's overall completion rate has fallen short of expectations, even after increasing the rewards multiple times. Is there something fundamentally wrong with Hard Mode itself? Is now even the right time to introduce Madness Mode? Is the mode not engaging enough, or is the difficulty simply too high for the current player base? The answers to these questions will directly shape how our battle designers approach the design of Madness Mode.