3) The Machine
In the trailer, we see several glimpses of the machine that looks to be responsible for giving Reed, Ben, Sue and Johnny their powers. We also see what looks like two different versions of the machine. One appears to be more rudimentary, and is occupied by a team of people in white suits. The other is more advanced, and shows a team in darker suits.
Also of note is the fact that there are actually six figures in the darker suits. We know from other glimpses of footage that our titular heroes don the darker suits, so who are the other two people? My guess is that one of them doesn’t survive the mission, and that the sixth is none other than Dr. Doom.
In any case, we know that the experiment goes horribly wrong. But we already knew that.