#1. PRICING
Pricing is, by far, the biggest reason why the population of the EU servers quickly died and resulted in multiple server merges. The main premium currency box, known as an L8000 on EU, is priced at $25. One of those boxes is basically worthless, because it requires dozens of them to really obtain anything of value. This is due to the very low enchant rates, lootbox rates, and special craft rates.
You simply have to drop huge amounts of money to get a single good item you need, and when you factor in the sheer amount of different p2w items in the game now, it is easy to see why it costs well into the 5 figures to obtain all the items you need in order to not just compete, but to actually survive more than 1 hit in PvP.
The fact that premium currency (L2 Coin) will not be dropping from mobs, means that paying money directly is the only feasible way to obtain access to this currency that will be required to create all the p2w items needed. No amount of farming will help you if L2 Coin doesn't drop from mobs. This could possibly still be okay if the prices of L2 Coin are extremely cheap, but I suspect that will not the case at this point. The price of this currency needs to be low, that way most of the players will be able to buy a large amount of it, and not just whales. Failure to have affordable pricing for the general population will kill these servers faster than you can blink, and this is by far the biggest death sentence topic in regards to player retention.
#2. Player Killing (PK) System
The current PK system will, absolutely 100%, result in large numbers of new players quitting this game. There was essentially zero penalty for mass killing of entire zones. EU/RU was forced to implement a small fix because the situation was so out of hand. But basically what is going to happen on these Aden servers, is a small group of players are going to go from zone to zone and PK every single char they come across. Lowbie zones included. This sweeping of zones will not stop, either. Every zone will get PK'd over and over until the players quit. Entire farming zones will literally be completely empty because the moment you teleport in, you will be instantly PK'd, and there's absolutely nothing that you can do about it. There will be people that spend all day PK'ing people, and they cannot be stopped. Even if you try to chase them down and attack them, they can instantly teleport away to safety and you won't even be able to touch them. There is no way to counter it. You will lose.
#3. Class Balance
While class balance comes in at #3, don't underestimate how important this factor is. Class balance in this version, and this patch that is coming to NA, is ABSOLUTELY HORRENDOUS. I cannot emphasize enough just how bad the balance here is. Dark Elf Death Knights, along with Titans, will run the show here. Starting with DE DKs, they are incredibly strong in all aspects of the game. They have a pull, they can blow you up in 1v1s, and they can AOE 1 shot entire parties and raids. If a clan here decides to roll mostly DE DKs, they will never lose a single siege. As for Titans, they run faster than you, they are unstoppable, they will keep you knocked down, and you will get immediately killed. There is zero counterplay for you against them. You just die, and there's not a single thing you can ever do about it. If they want you dead, then you are dead. This is due to the fact that they will have Frenzy and Zealot up, both of which last for a full minute and are on extremely short cooldowns, along with Knockdown, which has nearly a 100% land rate. In most cases, they will Rush you, instantly knock you down, and kill you, before the knock down even ends.
Every other class is pretty much irrelevant in this game. Sure, you need healers as well (Cardinal/SE) and even throwing in a few Overlords is nice. SWS/BD will be alts that are simply boxed and will stand and be left at the siege respawn points to buff up the raid before you make a push. But any clan that focuses on rolling only DE DKs, and Titans, will completely dominate the competition to the point that it will be laughable.
CONCLUSION
The PK system and Class Balance won't kill the game. They will severely impact the game, hurting the population badly, but not kill it. However, bad Pricing can and will kill this game. Whatever price you are considering charging for L2 Coin, I strongly urge you to cut that number in half. Even then, it might not be enough. I fully understand the mentality of the mobile game monetization model that is implemented here. I fully understand the aspects of targeting the whales and empowering them through this system. But you need to take a step back and look at the bigger picture. L2 so far has leaned far too heavily on the side of the whales, at the complete expense of the casuals/free to plays. You need to adjust this dynamic. Both of these players, despite being on the complete opposite ends of the spectrum, need each other in order to survive.
I have seen what can, and will, happen if you do not adjust course before this game launches. The players deserve better than that.