We have the Ultimate Quest to fight Masquerade and each time we beat the boss we can go up in difficulty. The JP version has another quest that has the same mechanics of beating the boss and proceeding to have a tougher version fight next round. This mechanic is great and adds a lot of replay ability to these fights as you progress.
However, if you've just started out fighting the base form with epic gear and finish the fight in seconds it starts to feel repetitive after the 10th fight that you finished off in record times. There should be a system in place where you can skip floors/difficulties that scales based off how quickly you finish the fight. For example, if you beat the boss in under 5 minutes you skip 5 floors. Between 5 and 10 minutes skip 3 floors. Lastly 10 minutes or over is 1 floor.
Plus more of these types of fights that scale in NGS would be amazing that has both solo and group content.