In order to say the most amount of things in the least amount of time, a trailer should have a narrative aspect I think, and tell its own story, through which the content of the game would be told. The trailer of Factorio
https://www.youtube.com/watch?v=DR01YdFtWFI was a masterpiece in this regard.
I think the start of the trailer should be the start of everything in Dwarf Fortress : the generation of a world. Ideally we see different possibilities of generated worlds : some have huge continents, others are made of island, and then we see other differences in topography or temperature. We see jungles, volcanoes, the formation of lakes, etc. All that in maybe 10-15 seconds.
Finally we stop on a specific world, and we see the civilizations starting to appear, to expand, etc. The name of the civilization appears on the screen and several events are displayed, we see the birth of specific characters. The age of the world is displayed, just as it is when you are generating a world. We see those civilizations trade, work, make societies, kingdoms and then wars. There would be dwarves, humans, goblins, elves, etc. All that in... 20 seconds maybe ?
After like 300 years, the counter of years stops, the screen make a zoom on specific regions to give information about them, their differencies etc (like "Oh ! This region has an aquifer !") and the screen stops on one of them, and it then shows the creation of a fortress. All that in 15 seconds i guess.
Then we sees the different identities of seven dwarves, their personalities, pasts, (ideally one of them is the descendant of a character named a few seconds ago, at the creation of the world) goals, and obviously their work. For the rest of the trailer, the game mechanics would be shown through them, their childrens, the migrants, etc. The seven first dwarves would make simple, great, and terrible things : one catches a fish, another plants some plump helmets, another kills a goblin, another becomes a mad noble etc. Many important mods may appear during all that, like dwarf therapist.
Could that be a good start ? I don't know if it would be possible to show the other modes, adventure/legends/object testing area, during that trailer. Maybe the adventure mode deserves its own trailer !