The marketing for Avengers: Infinity War held back Thor’s arrival in Wakanda and the Soul Stone quest on Vormir, and hopefully the Avengers 4 trailer also holds back some of its more crucial elements.
Speaking with io9, Kevin Feige said that characters like Black Panther, who disappeared in Avengers: Infinity War, would not show up in the marketing for Avengers 4, and I hope that bears out.
Part of the excitement of Avengers 4 will be seeing how Thanos is defeated and the mechanism that returns half the universe from the dead, and giving away too much of that in the trailer would do the movie a disservice.