Content Wise:
Not sure if it is too soon for more content or if more content is on the way.

I wish for more bosses that do not require Shadow Keys. Open an expansion to the inside of the core for more levels.
Perhaps add 1 more boss for every tier and rotate out with the existing ones in the arcade every time the elevator switches.
I'm going to try to give exploration to various enemies that do not have a boss form.
(Chromalisk, Spookats, Devilites, Grievers, Tortodrone, Gremlin King, Rebellious Knights, the Long Forgotten Z Slimes)

1 New Tier 1 Boss
2 New Tier 2 Boss
1 New Tier 3 Boss

Maybe offer 1 more boss after the Darkfire Vanaduke, like a swarm final boss. (another shadow key gate), that builds more story about the swarm.

Items:
Offer Weapons and Shield Transmutation the Sanctuary Alchemy Machine
(What do you think?)
Swarm type weapons. Almirian Mace (Stun and Fire). A 5* Darkfang shield line (increase the drop of darkfang shield). (I can't think of any ideas)

An alternative way to using trinkets, like increasing the chances of status effects or grant status effects.
Or a Trinket that gives you more movement speed or increase shield life or speed up shield regeneration. (not too much so that it doesnt make an invincible shield)

Accessories:
(Armor F or B) Side Arm (A holstered Handgun type) -->Like side blade (like a mini magnus)
(Helm F) Tech - Visor
Big Belt Bucket Type
Chains Type accessory

Gameplay Control:
Allow weapon specific auto-aim. Like say I want Antigua to have autoaim, but not Supernova. Mainly for the purpose of using a new weapon, allowing players try the difference between auto and no auto without forcing all your weapons to be all on or all off.

What do you think?