PLEASE POST YOUR OWN 
I have put together a compilation of ideas i have seen on the forum, excluding obvious bug glitches.:
1)Improved operatives:
Disguised as medic
When you disguise as a medic, you should be able to inject poison, they see their health buff, but it actually injects them with poison. the posion will take away 60hp(1/2 of a lights and 1/3 of a heavy) and will take its time effecting the soldier but with disorientation . you will also be able to throw lethal revive syringes and poisonous Lazarus grenades .
As a disguised Soldier
As a disguised soldier, you should give them ammo, they see ammo, but as soon as your far enough away or a certain period of time has gone, their Guns Jamm up( too big bullets) this only takes a few seconds to repairAn engineer can fix this for them or they can wait in a corner for a few seconds.
As a Disguised Engineer
And as a disguised engineer you can weaken their guns .but it wears off after time and if a engineer buffs their gun, it negetes it and adds what the engineer would normally buff them for.In simple, you weaken their guns but an engineer can fix and buff simultaneously
As a disguised Operative
Disguised operative : tricky: when the person your disguised as sees oyou. you dont look like them .So you look like another person to them(more importantly, not anyone that is neerby_ but theyre teamates will see double so be carefull
General aditions
also you should be able to shoot blanks to trick the enemy, these do no damage to ur team. if u shoot an enemy however, you lose your disguse and do damage.
These tactics are amazing in the heat of battle but given time are resolvable. Also adding a HE charge as an operative just adds a fake one which does not blow up .
Buff:enhanced Radar
This allows teamates to see enemies that have silent running from 50% further away(does not negate it but lowers its power a bit) and doubles your teamates RADAR Range.
2)more incentives to play as heavy/light
“Heavy- Immune to knockdowns
Light - Akimbo weapons (primary and secondary out at the same time, cannot ironsight, may fire primary with left click or secondary with right click)”
Thanks to:MonoxideAtwork
3)more SMART based maps.
There are hardly any heavily SMART based maps. most have some sort of SMART in it, but not loads, this would also tie in to #2 with more incentive to play as light
4)Symmetrical maps
There should be symmetrical maps.For example, a key in the center of the map and both teams need to use it to do something
Security:put in safe, escort safe carrier(theres other stuff in safe) to end point
Resistance: open prisoner, Escort prisoner to end point
Thanks to: i forgot his name :rolleyes:
New Weapons/Attachments
New Subcategories
Barrel: you should be able to edit the length and groove of the barrel to modify stability and range, amongst other things. they would be the following
ultra grooved long
ultra grooved med
ultra grooved short
Grooved long
grooved med
grooved short
Straight long
straight med
straight short
Ultra Grooved Super long(snipers only)
The longer the barell is, the more time it takes for the bullet to get out, meaning that more that one shot can be fired before it leaves the barrel, this means much more stability and accuracy for slightly less damage.
And equip seed.
the more grooved it is, means how clean the bullet flies through it, which allows more range but decreases
Rate of fire slightly.
Stocks
inspiration gained from: http://www.splashdamage.com/forums/showthread.php?t=30084
You should be able to customize your stocks, so you can choose from the following
Wood stock(Strong low recoil, less reload and equip speed)
Folding stock (med reload fast equip low stability)
Synthetic stock(faster reload, slow equip med recoil
Monopod Stock(snipers only)(more stability less equip speed)
Collapsible stock:Allows the gun to be collapsed, the stock has the same prefixes as synthetick, but when collapsed allows greater hip fire accuracy and movement speed(Slightly)
New Underbarelled attachments:
Bipod: able to deploy on surfaces, only for the gerund, rhett, (to emphasise the more offensive capabilities of the euston) , the sniper rifles and the LMG’s bar for gotlung. decreases vertical recoil, restrictive angle and lowers change speed.
Laser sight:Wait, this is a sight? no its not, it is put on the underbarell and it does the following:
removes crosshairs while hip fiirng, the bullet goes where the dot is when you ADS, the dot is also shown for improved accuracy. but you can be spoted easily and equip speed is slightly lost.(all guns)
Light shotgun: allows for a Masterkey to be put under the gun this is a portable pump action shotgun(assault Rifles and LMG’S)
Heavy shotgun: puts a sume automatic XM21 shotgun under the gun( compliable with maximus and chinzor)
Weapon Barrier: Uses a sheild from the mounted machine guns(the one in a V shape) it is liek weapon sheild but covers more of your body(Heavy weapons only)
flashlight: slightly disorientates enemies at medium range and blinds enemies at VERY clase range( due to the CQC feel of brink , this must be in their faces range 1v1)
More SOON!
These are just my 2 cents and other peoples.
PLEASE ADD YOUR OWN
Abilities for new ranks
Rank 6
Soldier- mortar. Throw a grenade that hits the ground and the area gets designated for a mortar strike.
Engineer- accuracy buffs. Engineers can throw buffs that increase accuracy and lower recoil by 5%. Can be self administered.
Medic- med kit. Medic can send out med kits that people can selectivly heal from, stronger than station but also limited resources.
Operative- cloaking (invisibility) operatives can be invisible but at the cost of walking speed, try to equip your weapon you’ll be visible again and last 45 seconds. Can cloak uav for 20 seconds. the faster you go the more obvious you are.
Rank 7
Soldier- ammo regeneration area, sorta like the new medic ability in the dlc but replenishes ammo, increases clip size and has a bigger radius. Last 1 minute.
Engineer- booby traps. Engineers can put visible lasers on the wall that when passed it. The lasers instantly shock the person Incapacitating them. They can put down a line of leaves that when stepped on grenades blow up incapacitating the victim. Both which can be disarmed and are very visible.
Medic- resurrection. Allows medic to revive dead bodies waiting for redeployment, they must walk slowly back to a command post to be fully healed or they are stuck on a cap of 1/2 health…
Operative- counter uav. Upgrades the uav so it will also jams the enemies radar by putting multiple dots on there radar confusing them. These dots will be close together following the uav’s path. Could be used to drag enemies from objectives.
New lvl cap 45. Could happen in a couple months.
New ranks.
Rank 8 abilities
Soldier: poison darts- last 30 seconds and takes away 1 hp per second
Engineer: Flamethrower turret- short range but well, flamethrower.
Medic: healing touch- melee a teammate to instantly heal them, allowed 5 times per two lives.
Operative: uav hellfire- instead of detonation as a attack option, the uav can also shoot missile, cool down with each successive hit. 2 per cool down.
Rank 9 abilities
Soldier: Trained mechanic- allows soldiers to create a small mg nest anywhere they please. 2 minute cool down period. New one will replace old one.
Engineer: rocket turret- a turret that shoots rockets, longer range than the gattling but low spread and weaker in CQC
Medic: new found strength- buffs a teammates muscle mass increasing accuracy, stability, and lowers recoil, can be self administered.
Operative: uav Gatling: a Gatling turret uav is now available. You now have the option to shoot missiles or spray pray enemies. 50 bullets per clip. Reload is 60 seconds long.
Rank 10 abilities
Soldier: claymores- like mines but slightly stronger and 2 allowed at once. Detonation takes 1.5 seconds. more obvious to see.
Engineer: assembly worker- allows you to fully customize your gun at the com station without a time limit.also replenishes half the ammo.
medic: think of one public? 
Operative: rc car- like the rcxd from black ops but just as strong as the uav but much faster and detonates when you want. also has a shorter fuse along with being more obvious.
original ideas from Baiken6609 modified by me.