Being the indecisive douche/dummy that I am, I have decided to make a list of suggestions rated as bad or undoable from the forum community. Along with brief explanations which may or may not relate to another Knight's reasoning.
I will not include guns with new mechanics or new monsters, but there will be exceptions.

Can we dual wield?
No, that would be too much power in your hands. Attacking faster can be chained with your possibly high attack bonuses will lead to extinction and annoyance.

Healing gun pls
No healing other players, no matter how slow, it is infinite health. Suck it up and start dodging!

Let's add a sniper!
Something that could shoot from outside a monster's projectile or attention range would allow enemies to be picked off extremely safely.

Forge sucks, remove it.
As Fangel said, in the days of Mist Energy we were limited by elevator fees and our daily energy to heat up our gear. Now you have infinite playtime (mostly) and it's up to you to use that playtime to be able to heat your gear.

Bring back mist energy this system sucks
Either yes or no to elevator fees, No. You should be grateful that you can find Alchemy Orbs to alchemize instead of arduously grinding 90k for a 5-Star hat.

Add Tier 4 and 6 Star gear!
That's too much effort to the devs and that will also split up Lockdown even more and it will make ultimate items less ultimate than they already are. What's next after Divine Avenger? Mega Avenger of Heaven +1?

Buff battle sprites. They're too weak.
Battle sprites are meant to mostly support your attacks or defense, not be the main force behind your damage.

We should have a permanent trinket slot.
Your Battle Sprite is your permanent trinket slot. End of story.

Revert to old display.
You want to replace shiny glowing weapons that make people strive to get them with blocky shapes that take about 2 minutes to form? And I know someone said something about knowing what their function is but come on, theres a wiki and a playerbase. Also, the health bar looked really weird.

Add a bomb that has a regular attack.
I thought bombs were meant to be charged up, walking into a pack of monsters and blowing them up or debilitating a number of them. Not just hitting about two enemies because that's easily possible with any other weapon.