Well here it is:
The stream showed off a lot of new features:
The new authority, Megacorporation, with its own unique civics much like Hive Mind and Gestalt Consciousness. They have a major penalty to going over your empire size so are meant to be played very tall. If you have a Commercial Pact with an empire you can establish Branch Offices on their planets for an initial lump sum of energy. These provide income to you based on the total trade value of the planet. As the planet grows you can build corporate buildings on it, providing bonuses to both you and the planet owner, so there are benefits to accepting Commercial Pacts from Megacorps.
A special civic available to Megacorps is Criminal Heritage, which allows you to build branch offices without other empires' permission. Their income is based not only on trade value but also crime rate - high crime planets are more profitable than standard branch offices but low crime planets will be less profitable. They have their equivalent corporate buildings which in addition also increase crime rate. The benefits to the host empire will still remain though.
Note that branch offices cannot be built in Hive Minds, Gestalt Consciousness or Fallen Empires. Each planet can only have one Branch Office, so Megacorps can fight each other to seize them from one another. Even if you revoke a Commercial Pact, Branch Offices will stay on your planets, so you need to declare war on Megacorps to force them out of your empire. But if you lose, they can make you a Subsidiary, a type of vassal that cannot be integrated but must pay 25% of their monthly income. Refusing a Commercial Pact will also give Megacorps the "Hostile Takeover" casus belli.
The civic Gospel of the Masses is also unique, and will boost trade value based on the number of spiritual pops. There is also a unique Temple corporate building which increase spiritualist ethics gain. This is the new Megachurch government type, available to Megacorps.
A new neutral faction, the Caravaneers, is always based in Chor's Compass. They have fleets which wander the galaxy and will offer randomised deals whenever they enter your borders. These deals can be a barter for a wide range of things (ships for pops, resources for tech etc.) which may be a great or terrible deal, given your current situation. Their home station is described as 'Space Vegas', where you can purchase premium currency (with in game resources, mind) to gamble with slots or lootboxes reliquaries. If their base is destroyed they may relocate to a safer part of the galaxy. There's no real reason to declare war on them, besides looting their caravan fleets.
Ecumenopolises are the result of a new ascension perk, and allow you to transform planets with only housing into an Ecumenopolis. This has access to much higher capacity housing and more efficient manufacturing/culture/etc. districts, at the cost of not being able to make use of natural resources or deposits.
There are 4 new megastructures: one that can be built around a black hole and provides a ton of minerals (Matter Decompressor), one that boosts fleet effectiveness and force limit (Strategic Coordination Centre), one that gives a big boost to unity (Mega Art Installation) and another which boosts diplomatic relations and immigration pull (Interstellar Assembly Centre).
The slave market is also part of the new DLC, not much talked about that yet other than you can use it to buy and free slaves if you want.
There are 3 new advisor voices: 2 corporate ones (one that's described as a cross between Zapp Brannigan and Cave Johnson, and another that's a more sinister 'Our customers are our family, our products a way of life' type) and a Shared Burden based one (pseudo-Eastern European 'Seize the Means' type).
I think that's about everything I saw on the stream. Honestly it feels like Le Guin/Megacorp is going to be a bigger shake up than Cherryh/Apocalypse, and that's saying something. It probably won't be as controversial though.
EDIT: I should also probably mention that Wiz has said that there's still some features they haven't talked about yet, so the above is by no means a thorough feature-complete list.
