This mod is amazing, but right now I'd say it's only good for a few hours of gameplay before you've exhausted all of its content. One option to fix this would be to add more content, but a simpler option that would do a world of good would be to give players dynamic ways of customizing their experience. To pick a few examples you could allow players to...

*Mix and match enemy types, such as making it so that every instance of a ballista is replaced with a Corite, or making every instance of a Corruptor into a Desert Spirit.

*Mix, match and disable biomes so that they appear at different points in the game than normal and use rooms from other biomes.

*Mix and match bosses so they appear at different floors than normal.

*Mix and match blocks, such as making it so that every instance of a dirt block is replaced with meteorite, or every instance of a dungeon block is replaced with honeycomb.

*Mix and match projectiles, such as making it so that every instance of a leaf projectile is replaced with a Phantasmal Death Sphere, or so that every instance of an Eye Beam is replaced with a Stardust Cell.

*Disable certain upgrades so that they can't show up during gameplay.

*Increase enemy health pools, damage, speed and attack frequency.

These changes may be difficult to implement but they would allow for the player-base to generate practically infinite content and keep the gameplay fresh long after they've exhausted all of its content. With those features it might also make sense to add an endless mode where each floor is harder than the last and randomly mixes and matches elements from the whole mod.