While Transformers: The Last Knight has completed principle photography and now deep into post-production, Paramount have some time to focus on the next movie in the franchise. The Bumblebee movie is aiming for a June 8, 2018 release date and according to Deadline the Paramount executives are pleased with the script turned in by Christina Hodson (Shut In). Hodson was one of the TF writer's room that developed the blueprint for the Transformers franchise for the next 4 to 5 years as Paramount attempts the Star Wars model of a film a year.
Hodson doesn't have much writing credits yet besides the just released Shut In film but she is seen as a Hollywood rising star with three "Black List" scripts (film insiders loving the scripts but for whatever reasons never getting green lit), wrote script for The Fugitive (that didn't move forward), and rumored to be working on the script for a Harley Quinn movie (which DC's fractured approach could never see the light of day). So basically we have no idea of her writing skill but a lot of people around Hollywood are putting in an unusual effort to change that.
Now that there is a script, the studio can now begin a search for a director who in turn will likely demand further changes to the script as the casting process begins. My guess is the film will be done on a smaller budget. If they reduce the Transformers cast to just a few vehicles, minimize their on screen time in robot mode and re-use most of the CGI assets created for the previous Transformers films, a budget of $100 million or smaller is feasible. Despite that they will still need sufficient time to complete the film so I figure they are aiming to start filming by summer 2017.