A hypothetical RH4 would have to be produced by a (mostly) different crew and take a different approach in order for it to be good IMO. For better and/or for worse, Bay is a auteur in his own right with the films he directs; and him not returning to the series was a significant factor that allowed the third Bad Boys film as we know it now to get made. (Likewise, this also applies to Transformers regarding Bumblebee).
Rumors frequently suggest Brett Ratner (who's directed the past three films) would be coming back if a fourth film does get made. And while I can't definitively predict who would be brought on to write the movie, I would personally highlight the possibility of him bringing back Jeff Nathanson (who did the story/screenplay for RH2 and RH3, as well as co-wrote Ratner's Tower Heist) to pen the story/script for a fourth movie.
If you let them come back to helm another movie, it will probably make Rush Hour 3 look like Beverly Hills Cop in comparison. I'd rather just leave the series alone. Come up with a spiritual successor if we really need another film of this type to be made.
