Dying Light 2 was first teased at E3 last year and Techland have said they'll have more to show at E3 2019. According to their Twitter: "We can't wait to show you the latest look at our most ambitious project to date."
The trailer we saw last year showed off Dying Light 2's branching storylines, which change areas of the city based on decisions you make. We know that Chris Avellone and Karolina Stachyra (who worked on the Bloody Baron questline in The Witcher 3) are involved, so hopes are high for the sequel's story.
One thing the previous trailer didn't show much of is what night-time is like in Dying Light 2. The clip accompanying the tweet, taken from the end of that original trailer, shows night falling so maybe that's what we'll get to see more of at E3.