Some small list of suggestions that I just felt like making.

• Auction House: Allow category exclusion filter - to avoid the listing spam in certain categories when perusing the catalogue. Functionally, you could make it work by going to "All" category and right-clicking on the other categories, it will exclude those from "All" instead of switching to them.
• Bombs: Truly sidelined for more than a decade now (exceptions do not disprove this), bombs can be made a new class of equippables and usable similar to sprite abilities (instant use but with cooldowns). This would require rebalancing them to utility instead of damage. This would also require modifying bomber gear, but I think instead a new grenade-launcher weapon class would reduce the negative impact.
  Concept of the G-Launcher

  EXTRA NOTE: to prevent the bombs from becoming over-prevalent, they can still be left to occupy a weapon slot instead of giving them their own slot. Another solution would be to have them with limited uses per stage. The G-Launcher would be exempt from suffering for these two possible changes, in the first, the G-launcher would be able to slot a bomb into itself so as not to consume two slots just for one weapon, for the second, allow the G-Launcher unlimited uses instead.

• Colosseum: While this has already received some attention, I was hoping it would be in the form of a wave-survival mode where 1 to 4 players would try to survive an indefinite waves of enemies, with X waves cleared making the players eligible for a Krogmolion reward and then every Y waves after that increasing the rewards. Failure to reach a wave milestone (where the reward increases) will cause a halving of the reward, adding an element of risk to the game mode. The wave balancing can be as so, reach 5th wave to be eligible for rewards, with bonuses every 2 waves after (The difficulty ramps up hard after the first 5 waves. This would serve for those who want a safe but slow grind and those who have to capacity to endure for a quicker reward)