So as we know, Hasbro and Paramount writers assembled an writers room for plan out the future of the Transformers films, the team consist of really talented writers such as Steven DeKnight, Christina Hodson, Lindsey Beer, Andrew Barrer, and Gabriel Ferrari, Robert Kirkman, Art Marcum & Matt Holloway, Zak Penn, Jeff Pinkner, Ken Nolan, and Geneva Robertson-Dworet, all of whom are tasked in coming up with ideas and storylines for the upcoming movies, so far we know three of them include 2017's Transformers: The Last Knight and and the untitled 2018 and 2019 sequels (one of them being a solo movie for Bumblebee), so the Wall Street Journal made an article about writting rooms and they revealed information about the process of the Transformers team
"On white boards, the group plotted possible story lines about an alternate history of Earth, from the time of the dinosaurs into the future, that imagined Transformers playing roles during events like World War II. Artists in the room turned ideas discussed around the table into visual concepts by the next morning. The group spent three weeks assembling story ideas and then, with the blessing of Paramount and Hasbro executives, split up to write treatments, or extended story summaries, over the next few months. The studio chose one to be 2017’s sequel “Transformers: The Last Knight,” to be directed by Mr. Bay, and another for 2018 that will focus on the character Bumblebee."
Also its worth noting that in the same article it was revealed that Micheal Bay is in fact not returning to direct the 2018 sequel/spin off after he's done with The Last Knight, and the studio is in search for a new director to take the helm.
We'll keep you updated when more information for the future of the Transformers franchise comes along