Marvel's First Family is long overdue for a big-screen outing. Thankfully, they'll be headed into the MCU within the next few years — either in their own film or via introduction in another MCU entry. While virtually all details relating to the Fantastic Four in the MCU are unknown (and likely will be for some time), it's safe to assume that two or more of their comic book adversaries will immediately join them on the silver screen.
Every film needs an adversary that embodies the plight of the heroes over the course of three acts, but it would be foolish to introduce a character like Doctor Doom in the first movie, only to have him defeated in 120 minutes of running time.
Send in Mole Man and his Moloids if Kevin Feige plans on giving the first set of Fantastic Four villains the Malekith treatment.
No, the major adversaries that have helped define the legacy of the Fantastic Four should be given ample screen time and their existence in the MCU should be felt for years to come. With Thanos now out of the picture, it's time to bring a new big-bad into the fold.