I'd like to see:

-the fleshing out of individual Transformers pasts using flashbacks to Cybertron

-Barricade is reintroduced in spectacular fashion by having him transform into robot mode while a human passenger (a policeman, innocently eating a donut and making a silly Baytastic joke) sits in the drivers seat. He does this infront of an Autobot (camera positioned to show barricade's lower torso in foreground with blood pouring onto the ground - Autobot can be seen between the gap in the background looking on in terror) who he then easily disposes of due to them being in shock.

-gun for hire, Doubledealer, has been hired by the Decepticons to take out human members of NEST - Optimus responds by calling for Nightbeat to come to earth to investigate/cautiously go after the (as yet unknown to the Autobots) villain whilst the rest of the Autobots focus on the remaining Decepticons

-a morally bankrupt bounty hunter in the vein of Lockdown who steals other Transformers parts (he's first seen repairing/upgrading Megatron's war wounds)

-Sam Witwicky in a coma the entire film (this doesn't need to be explained in great detail - maybe BB could rage upgrade to Goldbug at the same time)