So to suggest ideas about implementing sub-elements into the plugin could be some of the following:
Water:
BloodBending- Waterbenders could have a random percent when doing /bending choose water to have the "gift" of bloodbending.
Healing -The same could also apply for healing, not taking healing waters away completely but possibly a stronger effect such as regeneration two.
PlantBending- I think plant bending is fine as it is except could use some more abilities. In the episode of A:TLA "The Swamp" a "swamp bender" used the vines as protection while bending them and using them as an attack, I would love to see vines be better implemented into plantbending as it was a major role in the art itself. Possible new moves could be something such as vine armor or vine whip, etc. I would love to see more suggestions on how plantbending could become more in depth and have more functionality rather than just to use as another water source.
Rain- I've always wondered why can waterbenders not have an advantage during the rain? I personally don't think it would be over powered as to it doesn't rain to often and could be very useful in some instances. Rain could be a replacement source of water and have the exact same mechanics as having a water bottle except, without the bottle.
Icebending- Icebending was a new form of waterbending almost like earthbending introduced in the Legend of Korra. This could be simple walls of ice/packed ice created by a water bender if on snow or water/ice.
Earth:
LavaBending- I personally like the ideas that TehPandaKing posted, I think they were well thought out and solved many issues of the thought of "greif". The particles could make lavabending become more balanced and much more stable.
MetalBending- I also loved Zolteex's ideas once again for metal bending, I've already seen extraction which is very cool for server that do not involve McMMO. Having the ingot in your inventory would be a much more convenient rather than placing a block. The idea of iron armor could be a little over powered in some ways, could it depend on the amount of ingots you have with you to decide the amount/type of armor you get? Such as if you had lets say, six iron ingots, you would get the closest armor piece to that corresponding to the recipe, so a iron helmet(it would not be iron leggings due to that is seven ingots when you only have 6). And this could only last a certain amount of time and spawn with a certain durability knowing that it was not professionally crafted and was roughly made for protection.
Fire:
Lightning- The idea of redirection of lightning being horizontal rather than it magically coming out of the cloudless sky above you would be amazing. I am not sure of it would be possible in this version however due to there not being many or any vertical "beams"/lightning. However I did read in this thread that there would be a new particle/beam which origins are from the "Guardian" mob which is released supposedly in Minecraft 1.8. This would give lightning a new look and a better correspondence to the show.
Firebending- What would be cool related to the randomized chance of the water benders getting bloodbending idea, I think it would be cool that some firebenders have blue firebending. Although in the show blue firebending was shown by a "master" firebender(Azula) and was obtained by controlling/making intensive flames of extreme heat we can not implement a "mastering" system to the plugin as it would disrupt some server game play(if you disagree I would love to hear how we could as to this would add a whole new aspect on how to implement some sub-elements!).
Combustion- As to combustion I think it would agree to the randomized chance, but a much smaller percentage due to their only being one person with the ability. Yes there was another reborn in Legend of Korra but that could most likely be the daughter and or was born with the gift. Bending is all about the flow of chi throughout the body and its exit points so that is why they can blast extreme rays of energy(fire) through their forehead due to centering their chi flow there. Again returning to the main idea, the "combustion" sub-element could be a randomized chance in some firebenders when they choose their bending. I would not allocate this ability to only one firebender on the server because that special firebender could be only there for a minute/day or any amount of time and then become inactive. So I would personally let the occurrence happen more but allow it to be "rare" so that every firebender does not have the ability.
Air:
As of you to who saw my other post I love airbending and it is my favorite bending art in the show and in the plugin.
Spiritual Projection- As to this(only ideas that are roughly thought of and could always use improvement/modifications!) ability we could possibly add a move called "meditate" to better help an airbender connect with the spirits. As to the mechanics of this move, I'll leave you to the timers and modifications if this idea is selected as a possibility, you could meditate for a certain amount a time preferable a long one, maybe even on a certain pedestal or block structure. As you meditate you can not move until the move is deactivated and you could also get random messages of airbending information such as like "Airbending is the element of freedom" and etc just to give the player a little something while meditating. After a long period(possibly hours of meditation compared to your overall server time) you gain the ability of spiritual projection. In this action you could meditate(related to the idea of Zolteex of when meditating you lay down in the bed position and or a sitting possibly if possible, such as riding a horse) and when you activate the meditation move you could then leave your body and explore your surrounding area for a certain amount of time before you have to return to your body. To make game play fair, you could always have to find your body and if you don't, you take small amounts of damage until you do. Also during this state you can not hurt anything or the environment. To be more realistic you could possibly pass through walls? This could also lessen your time in spiritual form and due to the fact that you can not hurt anyone/anything you can not abuse this in pvp/raids. These are just rough ideas that anyone can modify to make it better suit the game play of a server. I would also make a system to which a player could not just sit AFK and meditate as to this would give many people the ability to use spiritual projection.
SoundBending- Possibly just a simple add on to the player of the ability to turn off your sound(if its possible with coding) of walking, breakage of blocks, opening chests, etc. This however could possibly be used for another move, such as projecting large sound waves that shortly stun the target(s) in a large radius(the farther the play the shorter the stun). The stun could be something like slowness or nausea. This ability could have a long cool down due to the power and effect of the move and the radius.
Chi:
As to chi, I am not very experienced with. If we are adding complicated sub elements such as LavaBending and MetalBending, that means we are entering the new age of The Legend of Korra. So a thought could be relative to the avatar state, we could have an amon-state or something of the sort. The Amon could be allowed as a donation rank/accessed by approval of a server owner or staff due to the new EULA. It would work similar to the avatar except it being Amon and with its different abilities. Most of you have watched the show and know the capabilities of the Amon having the power to take someones bending away completely, we could limit this to a set time such as twenty minutes to better suit game play within the server. The avatar could also restore their bending from the "Cleansed" effects as Korra did in the show.
The ideas of the Amon and restoration of bending came from the server game play of BendersCraft in which I am a MiniMod+ on, I thought this would be a excellent add on to the Project Korra plugin rather than having to modify Orions/make a new plugin.
Thank you all for reading my post, sorry if some subject were dragged on I am just excited to see Project Korra take off and become better. As I said in most of my reply, all these are just ideas that can be modified and change to help game play in a multiplayer server. I will leave this up to the developers opinion to use the ideas and or suggest how they could be better. However I would love to see the members of the site comments on how these moves could be used, if they are possible, different mechanics as to accessing a move, etc.
Again thank you for reading and I love feedback!
~Apple<3