We have pretty much seen the entire main cast list for the movie. There are the main roles and then there are supporting roles. Of course there are many more characters to cover and most of the fans want to see their favorite characters on screen but with such a giant universe of characters, it is hard to fit them all. This movie, we are treated to around 40 bots but unless it is a 4 hour movie, only 20 of them will have decent screen time and to narrow it down, only 10 of them will be the main focus of the movie. Alot of fans want to see their favorites like Wheeljack, Shockwave, the other Seekers, Hot Rod, Cliffjumper, Laserbeak, etc. and some people are hoping for some surprises such as characters showing up in the movie that weren't announced or had been spotted on set. So considering that we can only have so much, or few, characters in the movie due to the fact that we have to focus on a few certain characters, what would you rather have? 1) Character Cameos? - see them in the background, perhaps fighting the battle in the background such as in a big joint military Autobot task force, you see Wheeljack but he is not actually introduced officially. It is done alot in the X-Men movies and you subtley see them in the scene but there is no mention of whom they really are. Kind of like those Easter Eggs in the Star Wars prequels. 2) Minor Roles? - have them in non-speaking or speaking roles with few lines but only in one scene. They don't die and can possibly return in the next movie. Definitely more screen time than a cameo. 3) Quick Death? - they introduce a character but then they kill them off in a battle as robot fodder to make it more dark and edgy and to convey the message that this is in fact war and there will be casualties. This will include characters that we know from the cartoons such as Thundercracker, Skywarp, Huffer, or Tailgate etc. This is probably the only way they would introduce "other" characters compared to the ones we've already seen if the problem you have with the movie is "not enough robots" or "my favorite character was not there".