This is Just going to be a long post of things that I wouldn't mind seeing being put into action:

New weapon Lines:
Spear / Other 2 handed weapons - spears already have some image in the game as devilites throw them, using Spear to knock back enemies like the polaris does in normal attacks with a jump charge to jump in the area and slam down on an area

Dual Wielded swords - these have been tirelessly mentioned so I'm not going over them, however I do think the ability to forsake the shield for more damage would appeal to some, however, the game kinda centres around having one so might be too detrimental.

Bow and arrow - normal attack is a melee swing with the bow, charge attack is an arrow, 5* could have an enormous arrow fired, the Bow mainly centres around it's charge attack with Melee being to knock back, Charge attack should do more damage than a gun but the Normal should be a lot less, so essentially works as a charge gun would, this also makes way to such things as status arrows.

Change to Machine gun - instead of only being used against the trojans perhaps it should ONLY have a charge attack, reducing movement speed, however have the in accuracy of the normal attack, but with constant firing, a higher CTr allows for Faster charge up time to start firing, and higher ASi more bullets per second.
^ to add to this, you could keep the current machine gun and add a gatling gun which does as I suggest, could force all gatlings to have a movement speed decrease *which might also be an idea for the 2H and spear weapons*

More Levels, there are not that great a variety of levels in the game, with very few having secrets to unlock and learn, and usually only having 1 of those a piece, more levels with more secrets would be fun, perhaps limiting some secrets to certain weapon lines, such as a bomb being able to blow up cracked walls, or a gun reaching a trigger switch *such as in stone grove* or a whirlwind sword charge hitting 6 statues at once, or just 4 statues, hit at the same time stuff, not too many to overload people looking for them, but enough to actually make it more interresting, perhaps having the secret wall only appearing once in 10 levels that have instanced, so having an eye on your surroundings to notice secret cracks and switches would be good, as well as communicating a varied load out of weapons in the party over everyone just choosing swords and getting in each others way *one reason I determined to go bomber*
^ added, Puzzle rooms, not neccessary to complete, but if you can, treasure!

More tokens for diving Arcade bosses over mission ones, takes longer, more Me, should be worth more in my opinion, however I believe next patch brings in Hard modes so maybe this might be unneccessary after the patch

More bosses, again likely gone over and even more likely that it's already in the thoughts of OOO any way, but I'm adding it here

Side note MORE DANGER ROOMS< BRING BACK THE NUB SMASHER GIANT GREEN JELLEH

More PvP modes, I haven't checked but this has probably been covered in the forums before, Capture the Flag, Team Deathmatch, Team v Team arena Gauntlets, there are many that can be made and implimented, having only LockDown gets quite stale, you could even invite your own mode if you're creative enough, such as King of the Hill where you cant leave the area once entered and must gain points by killing as much as you can etc etc.

Premade LD and PvP line ups like in PvE, and no I don't mean GvG as very few people do that, just allow 2 or 3 people to line together and match them with others lining with friends so they don't end up fighting each other

Guild amenity - design a gate - a guild arcade gate where they choose what levels appear inside, only 1 per guild allowed, to calibrate it they must use their minerals to do so, gives incentive to farm them. the gates starts with Tier 1, can be opened to tier 2 and tier 3, each week it gets reset to each depth containing 5 levels on ? setting, removing a level costs so much mineral, so does adding a level, and so does removing the ? setting, this could also be made into a Ce or Cr dump aswell, as a good guild could craft a very good arcade to dive for Cr so it should balance out so that it does not effect the Ce market

Get in on the Trading cards things on Steam, I'm not sure how the companies work together to sort this, but TF2 has joined in and SK has in the past done joint things to TF2, so only seems logical to join in on steam cards to.

Reporting - allow the reporting of beggers
I actually like the community overall on this game, it's unfortunate that in most online games now a days you get the Troll/flamers ruining people enjoyment, and I find luckily this game doesn't have many of that *though in PvP it does sometimes rear it's head* however, Beggars are annoying, I don't mind people asking for help, but constantly getting trade requests and GIVE ME 100Cr! PLEASE PLEASE PLEASE PLEASE gets annoying, and you get this almost everytime you enter haven.

Upgrade to Punch, instead of random, allow the purchase of specific UVs and rank for certain Cr, this might be undesirable, overall, but I find being able to make my sets of weapons as powerful as possible without having to click 1 UV over and over until I get the right one better, make wanted UVs cost more, with higher ranks multipling, so say ASI, is 10k as a base low x 1 med x 2 high x 4 VH x 8 and Max x 16 *max only for armor just as an example*
so 10k, 20k, 40k, and 80k, *these are just example numbers and would likely want to go higher*
^ what might be good is keep the random version but add the selected on top of it, but at a steeper price, so you can risk a random one, for cheaper, good for the newer players, but choose exacts for mr money bags and the veterens out there

I haven't gone into too much detail into these, as I'm not a game designer, I am not specialist in balancing things, these, are as the forum states, are merely suggestions.
However I wouldn't mind hearing other people opinions on these ideas and thanks to anyone that has taken the time to read the entire thing