It's confirmed. Michael Bay is back for Transformers 5 and it was obvious. He directed the Transformers movies since the first one. I remember that every body were amazed from it but then came the sequel and then the second sequel and then the third sequel and millions of people understood that Bay is not the right director for the transformers movie franchaise. Now when he is back as a director again I'm expecting many but I think the final result will be something really bad.
We also know that there are rumors about Shia LaBeouf and Megan Fox returning to the franchaise. For me this isn't very good but we'll see.
Another huge bit is that the Quintessons are set to possibly appear as well,the Quintessons are the creators of the Cybertron natives. The other newcommer is Ultra Magnus which is going to be Optimus Prime's brother (depending on which continuity we’re talking about here).
Transformers 5 will be realeased in 2017.