A World of Skills
It might already be too late in the game development, given the choices already made, but here are some ideas...
Imagine a game world where players have to hunt down the skills they want their characters to have. Where the initial skill for all players would be just a basic Punch (very weak) and, for everything else, they would need to learn from questing and interacting with the world.
There would be no pre-set classes and all skills would not be fully disclosed upon the start of the game (your skill list would have just 'Punch' in it).
To learn new skills, players would need to find teachers or masters (NPCs) in the world and either pay them money or run a few quests for them so you can learn the base version of that skill. This would apply to all skills in the game: active and passive skills, magic, melee, healing, tanking, crafting, movement, and so on.
All players could potentially have all skills in the game (if they hunt for them), but only a limited number can be equipped and used at any point in time. If the player equips more than one skill of the same school/type, they would earn a bonus on the skills of that school/type, incentivising specialisation when playing in groups. (kind of a 'soft' class system but allowing the player to chase and level up new skills and change their playstyle with the same character)
The world would have hundreds of skills to learn and find. Each with their own background story, big or small. Each skill would have its own XP bar and could level up, growing in power with use (indicating that the character gets more 'practice' in using it, like in real life).
Different regions of the world could have different skills to learn and skills could have synergies with other skills. Just imagine, in AoC, players would need to level up a node to be able to get the right NPCs there to teach them a good/rare skill. Dungeons could hide unique masters or bosses which might be a source of a new skill.
The easier skills, such as sword fighting or magical light can be learned from common NPCs in schools in most cities, but more powerful skills, like Meteor or Tornado would need to be learned from more difficult areas and going through harder/longer quests or quest lines.
Imagine that, for learning the Fireball skill, you would need to visit a village of fighting mages in the desert, find the local master in the Fireball art and run a few errands for him, which would actually be tasks that have some meaningful connection to that skill, such as observing and fighting fire-breathing lizards or challenge 5 different NPCs in the area, each one, when defeated, giving you a different tip on how to 'concentrate' and 'feel the fire'. When all are defeated, you go back to the Master and he 'puts it all together' teaching you the Fireball lvl 1 skill. This skill then just pops in your Skill list, so you can add to your action bar or hotkey.
Some other skills could only be obtained by going up in rank in certain NPC guilds or when you reach certain level of affiliation to a faction. The master of that faction/guild could then teach you that skill when you achieved that new rank.
You could also get some skills from fighting mobs that have that skill (your character would be learning it from 'observation'). Say, for example, you fight several bandits who Shield Bash you. If you have learned the basic Shield skill and fight enough mobs who Shield Bash you, you eventually learn it.
In this game, players would rely on the community/internet to learn about secret, fun or powerful skills and how to get them. Future versions of the game can launch a bunch of new skills with related quests and NPCs, and people would need to get back into the game to hunt for those.
Just imagine when you see another player use a fancy skill in battle that you didn't know about, this would be a conversation starter: "Where have you learned it? Where do I get this skill?". You would just have to have it. Players could also be incentivised to help other players get that skill by getting extra XP in that specific skill when they complete the same skill quest while they have a player without that skill in the same party. Skills could also be randomly learned from fighting a considerable time alongside other players in the same party, if they use that skill many times and your character has enough level in that skill school.
You could find out about different skills to learn and 'class builds' by reading in-game books or talking to a few teacher NPCs, but many other skills would need to be discovered in the world or via the community.
Even as the game would not have any 'hard' pre-set classes, the game could still have different races, with different starting stats, but all skills would be acquirable from the game world, by all players. (Although there could be some race-specific skills, acquirable from race-specific quests).
In MMORPGs, what most attracts me is the feeling of character growth. Getting new skills, new mounts, new gear, and becoming more powerful. Being able to do more, reach farther, kill bigger mobs with every hour I spend in the game. In real life, self-development takes years, it is frustrating and very hard. In a game, especially MMORPGs, developing yourself takes minutes and you get constant direction and positive feedback. If you can turn the whole game into a hunt into self-development, where you can hunt for better skills in the world, following stories related to those skills, and the masters behind them, they will mean something to you. And there will be a good reason for your friends and the community to help you, in showing you how to get their cool new skills while levelling up themselves in it. Maybe some skills would need two or more players to be acquired or even used (those would be powerful boss-fighting skills).
What do you think about it?