Social interactivity system
Plugin idea:

In order to get people to do more as a community instead of just going their way solo, there should be a system to make it a necessity to play with others. Elements of such a system may include a leveling tree that is linked to a profession/class a player may choose before starting his journey. Upon joining a server he will be promted with a choice to select one of a few jobs. These jobs/classes could be:

Miner
Smith
Farmer
Shaman
Warrior

Each and every class has its own skilltree that can be progressively unlocked when mastering certain skills and or bny collecting exp passively when doing their job. As such, each skilltree comes with perks but you also always have to make a decision between two so you get a pro but also lose the possibility for another perk.

Perks may include:

Miner=
[Deep-Mining]: When mining in areas lower than 40 blocks above bedrock, players with this perk can still mine normaly. Players who don't will receive fatigue and blindness (as if they can't deal with the deepness, pressure, humidity and heat)
[Vein-trigger]: When mining multiple blocks that are connected in a vein, this perk allows you to gather them all in one go.
[Quality]: The higher this skill is, the higher the quality of the mined ores will be. This will affect quality and quantity equaly. This is important when combining this with the job of the Smith. Higher grade materials can be forged intop higher grade weapons, tools and armor (but also require a higher crafting skill for a smith)

Smith=
[Extraction]: Allows a smith to extract fragments like gold ingots and "iron nuggets" from certain stones.
[Analyze]: The skill to analyze higher grade materials such as better wood, more pure iron or higher graded diamonds. This allows them to combine them into higher graded tools and armor.
[Workflow]: When crafting all players will receive cooldowns acting as their limiting factor for how much they can work. Smiths for an example need to learn how to crate quality weapons and from ttime to time a forging process may break and the desired tool or creating will not work properly (it breaks instantly). On the other hand, they can skill their workflow, allowing them to reduce the cooldown as well as the ammount of deteriorating items they craft.

Shaman=
[Enhancement]: Collecitble from plants all around the world shamans can find custom ingredients, They can then combine them to create enhancing items with which they then enhance other things such as materials or food. Higher quality food means more restoration and gives a boost on moral.
[Boosting]: Boosting allows to enhance the moral or wellbeeing of players of the group of the shaman. This gives them positive, random perks like strenght, nightvision, speed 1 etc. Bad nutrition can have the opposite effect.

There are many many more implementations of such skills and ideas but the base idea of all of this comes down to make people work together to create more complex social structures. This could also be benefitet by mechanics such as buildings that can be created by the community, then placed as a structure block that will unfold and give the society access to new elements such as unlocking better skills, unlocking more resistant crops etc. It could also give them boosts like more battle-skills for the warrior class if the town/city has unlocked structures such as a training barraque where they can train their battle skills with a boost (the higher the level of the barraque, the higher the boost). The higher the level of the warrior class, the better walls a town can place. The better walls it has, the more inviting it is to become a public market. The bigger the market gets, the more npc traders will travel to the town, offering exocitic or high level things such as resources, skillcards, plans for buildings etc. Enhanced farms may include an automatic watering system which will give boost to crop growth.

I hope you could grasp the idea of the system at least a bit by now :P