It has to be a soft reboot. Bumblebee is critically acclaimed, profitable and has built up so much goodwill. It also provides the perfect opportunity for future films to retcon the Bay movies.
Paramount have finally stumbled upon a formula that works. Character driven, well written stories, good direction, action sequences that can actually be followed. This has to be the template going forward. A Bumblebee sequel featuring one or two more Autobots, maybe a solo Optimus Prime movie. Use these to flesh out the story of the war on Cybertron, while building the robots as characters. Then you can look to do another team up movie. But look at the mess of the DCEU for an example of what happens when you rush into cinematic team ups without the audience being familiar or interested in your characters. Bay was only able to fit so many "characters" into his films because the robots were mainly 2 dimensional and lacked character.
Hasbro will want a strong Transformers cinematic franchise to help push their upcoming Hasbro Cinematic Universe.