Mister Fantastic's powers were the only ones missing from the first The Fantastic Four: First Steps trailer. That led to many theories about why they were not shown. Recently, Marvel released a new trailer that featured a snippet of Reed Richards using his elastic powers. I think there could have been two reasons why Marvel did not show them at first. Either the studio found them to look goofy compared to the others, as happens with that style of power, or since Reed's powers are the hardest to make look good, the VFX team needed more time to perfect them.
