Mini-campaign, single player modes
What if they released a mini-campaign of 3 or 4 missions that are simple and brief, not big budget high production value, that explores the 2042 environment and story. They could showcase some of the specialists' abilities and possibly have a co-op part that involves them working together and coordinating. If it does well they could release another set of missions and continue doing this till there are a good amount.
In addition to that, they could make a set of mini-challenges/mini-tutorials for single player as well each with a number of levels that increase in difficulty, examples such as tv missile going around obstacles to reach end target; nightbird dodging tv missile eventually having to dodge multiple missiles coming both consecutively and at once; select number of weapons/vehicles used to shoot down tv missile, falck using healing pistol to keep a minimum amount of teammates alive in a fight with the minimum amount increasing every level, straightforward sniper range with target getting smaller and farther and shooting multiple targets; etc. This could help to train players and get to know how to use different things in the game in the form of a challenge or minigame. And there could also be a timer or score at the end of each level that gets posted on a leaderboard online to show how well players did in each challenge.