I'm torn.
I would like to find a way to wrap the Unicron teased story up in a concluding TF6.
However, with the "make it up as we go" screenwriting that the Bay-verse writers have given us for 5 films we may be better off without that film. Their TF6 might leave us with just as many unanswered questions as we currently have.
I'm totally fine if Bumblebee is a prequel series. I know they've now said, reboot, but that was after the fact. It is clear they crafted BB to try and have their cake and eat it too type deal by now saying, reboot, while being coy about that before.
Solid writing could align BB prequel series with TF-1.