My guess is not to expect an FF book until the sale is approved. Which is months away as it needs to go through the Federal Trade Commission.
While it's probably going to take most of 2018 to get the deal done, I can't see a reason why cranky old billionaire Ike Perlmutter would care if Marvel went ahead with a Fantastic Four title.
Noah Hawley says Doctor Doom movie still in development
On a side note, Noah Hawley (Legion, Fargo) says he's still going ahead with his Doctor Doom solo movie and will finish the script when he's finished writing the last episode of Legion. So that leaves things in a gray area on the film side of things if they can still come out with a Doctor Doom movie treatment while the sale is being finalized.