All human action has eschatological foundations. God created us to face the future, and that is where we are all going, like it or not. This means that any task that we undertake is going to have some eschatology associated with it, either express or implied.
If we try to deny this — by pretending to have no interest in “end times stuff” — then this just means that the work we do in Jesus’ name will be shaped by an eschatology that is alien to the Christian faith. That eschatology might be Marxist, or one of consumerist progress, or environmentalist doom, but whatever it is, it does not culminate in the knowledge of the Lord covering the planet as the waters cover the sea.
So in order to be vibrant and healthy, I would argue that missions must be overtly and explicitly optimistic in its eschatology. Your eschatology will shape the day-to-day nature of your mission. Your eschatology will determined whether or not your evangelism is of the man-the-lifeboats variety, or one more conducive to culture-building. And culture-building is being used here as synonymous for “discipling the nations.”