Sorry for the long post, I attempted to put together a better list of what we know so far. Feel free to add, modify or correct as needed as Im sure I forgot stuff. Hope it helps a bit until we receive official patch notes.
Outer Rim General Info
Outer Rim is considered "close quarters" pack
4 maps Jabbas Palace, Jabbas Sail Barge Garage, SoroSuub Refinery, Sorosuub Pipelines.
All modes are 8v8.
Outer Rim will work like a playlist. You can select a game mode (Extraction, for example), but after the 2 rounds are over it proceeds to the next game mode. Dice has said generally speaking, playing through the entire playlist takes approximately 8-10 hours.
Greedo and Nien have sliding scale traits. In other words, they level up as you get kills.
Niens abilities Anti-infantry turret. As you get kills, it levels up to explosive shot. Has Pulse Cannon with fast cooldown. On small/indoor maps his last ability it proximity mines, he is able to plant 4 at a time. On large/outdoor maps, he has Orbital Strike instead of mines.
Greedos ability (corrections may be needed) an ability similar to Hans Lucky Shot. Grenades can level up grenade type as you get kills. Level 1 is Dioxsis, level 2 is Thermal Detonator and Level 3 is Imploder. He also has some sort of multi lock-on one shot infantry kill ability. Greedos abilities can also decrease (level down).
New Star Cards (exclusive to DLC) Dioxsis Grenade, Adrenaline Stim
New weapons (exclusive to DLC) Scatter Gun, Relby V-10 semi-automatic rifle, Greedos pistol
Greedo and Nien are in MP modes only, but will be patched in SP modes at a future date.
Hutt Contracts
New Star Cards can be purchased through Jabba. You must first purchase the contract with credits, then you are given in-game requirements. After the requirements are met, you get the new card.
Dice has confirmed that all future free Star Cards will be accessible via Hutt Contracts.
Everyone gets access to two weapons without Outer Rim DLC the DL-18 and DLT-19x
Game Mode Updates
Team balancing will transpire when map changes.
Dennis alluded to breaking up parties and putting them on opposing teams if necessary for balancing.
When playing as a Hero in an objective-based game mode the Hero can indicate which objective he/she will pursue via an input command.
New level cap is 60, reaching Lvl 60 will unlock Weequay skin for the rebels. No Imperial skins this release, but more are coming in future releases.
Combat Roll - soldiers and some heroes can now perform an evasive combat roll by strafing and double-tapping the crouch button (consoles). All soldiers can combat roll, as can the following heroes - Han, Leia, Nien Nunb, Greedo.
A spectator mode will be implemented in private matches - 1st person , 3rd person, free camera and hudless modes for cinematic capture.
Vader will be getting a buff the changes we know of is his block time will be increased from 4s to 8s, longer saber throw and increased health.
Quick Match options - can matchmake by multiple game sizes 12, 16, and 40 player games.
Extraction
Rebels must escort the cargo through checkpoints. Each checkpoint has a time limit. If the cargo is brought to the final checkpoint, the Rebels win. Otherwise, Imperials win.
If you get the hero pickup, the hero is chosen for you. More than one hero can be present on each team, a new team-specific hero pickup appears as time passes and phases of the game progress.
Rebels will get a hero in first phase and strategy will be to stay alive for future phases when Imperials get heroes. Dennis stated Vader will be 3rd phase villain for the imperials.
Heroes vs Villains
You now choose your hero.
Outer rim is 8v8 with 4 heroes on each side, vanilla content remains 3v3 but the new heroes are selectable.
Only 2 Honor Guards/Shock Troopers will spawn per round.
Hero Hunt
New method to become Hero in Hero Hunt the top 3 damage dealers to the hero are given a chance to become the hero via a wheel of fortune. Your chances and section of the wheel are determined by how much damage you dealt. The person who is chosen becomes the hero, then there damage to hero resets, while all others keep their damage dealt.
Fighter Squadron
Ramming change when ships of the same size collide, both will die. If a small ship collides with a large ship, the small ship dies.
Weapons and Star Cards
Scatter gun pierces personal shields
Adrenaline Stim triggers regeneration immediately
New power up (for all players) Ion Disruptor. Charge weapon that looks immensely powerful and can kill multiple enemies simultaneously. Effective against all vehicles and turrets.
Barrage will be getting a buff.
Grenades and Missiles no longer go through squad shields. Cycler, Scattergun will still pierce shield and Ion Grenade will auto nullify it.