The new trailer also hints at a bit more of the storyline: the President of the New United States is visiting Night City (which is independent of NUSA control) but shenanigans ensue and they get in over their heads. V is recruited to go into Dogtown, possibly the old Combat Zone, a chaotic area of Pacific where anything goes (this area was sealed off in the main game), where they liaise with Reed on a mission that is said to be influenced by spy thrillers (with more than a whiff of Escape from New York to it).
New content in the expansion appears reasonably generous, with a new storyline extending across multiple main missions and side-missions, along with new characters and weapons and a new district of Night City to explore. The expansion will also apparently open up existing areas of the city for you to visit, including the large stadium visible from across the city which was also unreachable in the main game.
As well as Elba joining the cast, Keanu Reeves is back, having recorded new dialogue as Johnny Silverhand, V's reluctant cybernetic head-guest. It looks like the expansion will make use of a save set before the end of the main game, rather than following on from the end of it.
CDPR have indicated that the expansion will be generous in size, larger than The Witcher 3: Hearts of Stone but not quite as big as the massive Blood and Wine expansion for that game. At the moment they are only planning one expansion for the game, having scaled back their plans for multiple big expansions due to the original game's troubled release and the need to extensively patch it. However, the game has enjoyed a significant critical renaissance in recent months and a boom in sales that have passed it over 20 million copies sold.
Phantom Liberty does not have a firm release date yet, other than some time in 2023.