It seems that the fourth film in the Cloververse has been confirmed to be the movie 'Overlord', and the movie has already been filmed! There was some speculation in early 2017 that this would be the case, but the rumour was not confirmed... until today.
Overlord is reported to be a World War II mystery/thriller, starring Wyatt Russell (who previously worked with Dan Trachtenberg on the Black Mirror episode 'Playtest'), Jovan Adepo, Bokeem Woodbine, Jacob Anderson and more. The synopsis for the movie reads:
"On the eve of D-Day, American paratroopers are dropped behind enemy lines to carry out a mission crucial to the invasion's success. But as they approach their target, they begin to realise there is more going on in this Nazi-opccupied village than a simple military operation. They find themselves fighting against Supernatural forces, part of a Nazi experiment."
Overlord is directed by Julius Avery and is set to release October 26th of this year, but considering the delays on the third film and the fact that there is only a matter of months between the two movies, it would not be surprising to see Overlord delayed, possibly into 2019.
The premise of having a Cloverfield film that is set before the first movie will be a new and refreshing instalment in the series, perhaps providing some backstory or origin to the first film.
While the movie has been wrapped under a heavy layer of secrecy, like all both Cloverfield movies before it, some pictures of the set & cast have been uploaded to IMDB. You can see those photos here. Some pictures were also also found coming from the crew of Overlord (via Instagram), presumably when the film had wrapped. They used the hashtag #overlordmovie.