it would be set many years after the third movie, the autobots finally share their technology with humanity and it pushes mankind way too fast as multiple companies try to colonize mars and are making weaponry that has every other nation scared
in the first movie there is a cult that has been appearing around the world. they are tied to one of these corporations sending probes into space. it is revealed that they are in contact with a race of machines that originated from cybertron, a group that even the decepticons, whom they spun out from are afraid of.
they sent these probes into space to try to summon unicron to earth to destroy it. and he has sent scourge and his sweeps to earth to help "prepare" humanity
they use the technology the autobots gave them to weaken earth's defenses and weaken us before unicron arrives.
for a sequel id have Galvatron arrive on earth seeking revenge on optimus for his former master megatron and scourge. we also reveal he is being controlled by unicron as part of some deal they made and after earth was destroyed he would be let go of this deal.
also the quintessons show up, they would look the way they did in the cartoon with that shellfish ship that i loved in the original.
they hint that unicron was a creation of theirs who developed a mind of his own and they want to put him back under control so they can use him to keep their "colonies" scared and they dont care if earth is derstroyed in the process
the third movie is a 3 way battle with the humans and the autobots, unicrons and his sweeps and the quitenssons and their sharkticons battling for earth
a few other things i would also do:
1. i would have the autobots keep a more 80's toon look while the decepticons keep the look michael bay gave them cause i think it looks kinda cool on them
2. galvatron himself would be something like this
. he would transform into a tank but also a cannon and his laser is extremely deadly
3. i would bring back this character from beast wars for it, he is an assassin for the quintessons, murdering humans who try to fight back their occupation. he just looks way too badass to not put in
4. bring back characters like arcee and not have the transformers be so expendable like they were in the last 3 movies. also metroplex, hot rod (he wont become a prime
) kup and ultra magnus
5. i'd bring back characters like predaking, scorponok (this version would be the size of a building) and trypticon, who are used by unicron to keep the population scared, then the insecticons and ravage to assasinate any one who tries to stand up to them
what do you you all think?