If I were lead dev, these are the changes I would pursue initially depending on player support. I would immediately work towards altering the cash shop focus, make combat more interesting, focus on PVP game play since it adds the greatest re playability, and revamp the UI.
Changes to cash shop model:
There would be 3 changes. How you use the cash shop, equipment, and removal of pay2win elements.
Through the pay gate you will only be allowed to purchase points. You won't be able to subscribe through the pay gate. Instead you would subscribe through the item mall screen. I think this simpler setup would make getting points easier.
On equipment, I would like it to be a collectible. A person would go out and collect as many armor pieces as possible. They can store it as a set for quick moving and equipping. A few of the items to store the equipment will be given for free with the rest purchasable through the cash shop. In order to make it a collectible, the equipment would need to be balanced against each other. They would be good for doing a particular task or fighting a particular opponent. They would not necessarily grow with levels, just get more specialized.
Equipment will be upgraded differently to remove the pay2win elements.
Compounding - Creation of equipment from parts, always a 100% success rate.
Reinforcing - Like the old system, 5 levels of upgrade. Never a chance to break or degrade, success rate 100%-50%.
Enchanting - Enchantments can be compounded to be stronger. They can also be removed from equipment at a blacksmith for zeny.
Raid drops will change. I want everyone to get something from a raid, not just a couple people. If the raid party completes the raid with half as many people, I want them to get twice as much. To this end, the raid drops will be ingredients towards compounding. This way players can collect a set within a reasonable amount of time.
On pay2win elements. Several items will be removed from the cash shop and put in game as drops or purchasable. They are the potions, atmas, several mounts, lucky boxes, and success rate xeons. Mounts and Costumes will become permanent for 1000 points with no bonuses.
Changes to combat:
My goal is to make combat longer, strategic, and more rewarding. Here is a quick summary of the changes. The player will be able to choose soft targeting or the current targeting. Soft targeting will have a crosshair and 2 targets. The last ally and the last enemy targeted. When the player does something it will target the most appropriate one last targeted by the crosshair. Like a heal will hit the ally, and an attack hit the enemy. Melee will use arc targeting. Everything within a 4m arc in front of them is hit. This is to make up for the range disadvantage, and the damage is split across all targeted foes. Some changes may be made to address potential issues.
Survival combat. I want engagements to be long and strategic. To this end I want HP/MP to increase a lot, Damage to decrease. Charges for powerful skills. None of it replenishes automatically. They will have a limited number of recovery items. So in the end the player has to manage what they have and decide how they will engage a situation. At certain safe areas their HP/MP, charges, and recovery items replenish. In order to compensate for the increase difficulty, the XP and loot gains will be increased dramatically. No longer will the player have to kill a legion of monsters to progress. Instead they will face a couple dozen in the same amount of time.
Removal of support roles. I want to eliminate the waiting for a tank and healer syndrome in the mid-game currently. I also want all classes to be able to play in the gamut of game play. Solo, Group, Raid, and PVP. I don't want them to be relegated out of certain game play aspects. The support role will instead be spread across all the classes.
Removal of [Insert verb]-er class names. Some of them fit, some of them are lazy Korean translations. I would like the community to pick their class names, If they like Hunter that would be cool, if they change the name that would be cool too.
Removal of race restricted classes. To me the race restrictions create overlap of class skills where they should not exist. A race should have a couple general attributes, and class its own attributes.
Usage of 4 class archetypes with 4 classes each: Control(inhibiting an opponents actions)[Defiler, Avenger, Tempest, Forsaker], Combo(Increasing damage by creating situations)[Berserker, Protector, Elementalist, Assassin], Augmentation(Enhancing/Changing self to alter the situation)[Radiant, Mystic, Druid, Soul Hunter], and Pet(Using numbers to win)[Dominator, Hunter, Commander, Warlord]
ALOT more skills. I want enough skills to create builds and trees within a class. I also want to avoid more than level 5 in a skill.
DNA collectible and can be changed at NPC.
Changes to PVP:
Battlefield points combined, with combined reward shop.
Two types of battlefields: Common and Event.
Common battlefield type rotates daily. Events are available a couple times a day. This way some variety is created
Addition of new common PVP modes, FFA, Capture the Flag, and Ladder.
Guild wars added as an event battlefield.
Reduction in the amount of actions needed to PK other players.(You should be able to respond immediately when someone is attacking you)
Addition of Guards in town to reduce PKing in towns
Changes to UI:
Reduction in skill slots.
Ability to chain skills(When you click 1 for a skill, you can click 1 or 2 for a different skill in the chain).
Use a vector based font to reduce blurring.
UI contest to get ideas on a good layout for all the little icons around the screen.