Why not Captain America

He will be busy reprising his role in Captain America The Winter Soldier while Bay is directing the 4th film

 

Because he isn't an Avenger and he isn't even a Marvel character.

 

An interesting prospect, but one that I think works best if we simply use our imaginations and imagine what could come of this, as the chances of it actually happening are slim to none.

1.) There's the same chances of RDJ as Tony Stark being in TF4 as there is a chance of me chugging a carton of milk through my nostrils. That is to say, not very good chances.
2.) Now, why only "one of the 5 out of 6 actors"?  
3.) Jon Voight, Frances McDormand and Patrick Dempsey are all "serious actors that [didn't] act stupid". And if they're in a Bay film, what makes you think they won't automatically act stupid? Would their experience in the MCU suddenly cause them to not be under the influence of Bay's directing style/choices? "I've worked with Joss Whedon. There's no way I'm saying "Shoot that motherf- Whoa!". I may be in your movie, Bay, but I have standards!"
4.) I'm not against the idea as a fan (because there's a lot of potential, visually speaking), but realistically, let's just have MCU and Bayformers stay in their own, separate universes, shall we? (Outside of fan-fics.   )

This.

And also this.

 

I think that people forget there's a team at times, and it's not Iron Man and Friends.

Anyways, Chris Evans. He, Mark Ruffalo, and Coulson guy were amazing.

 

Good point. If Decepticons like Megatron and Starscream can be killed by Sam who lacks any sort of combat training then what chance would any Decepticon stand against someone like Iron Man, Thor, or the Hulk?

 

Forget them we need to get Andrew Garfield's Spider-Man in this so he can help team up with the Autobots like he did in the Marvel comics.

Prisoner of War! - Transformers Wiki

 

black costume spiderman with gears and the autobots.

 

We don't need more Avengers, we need more Robots (that are actual individual characters instead of generic troopers).

 

Where's, War-Machine? He's not exactly part of the team, but he is one the side characters that comes in and helps. I'd vote for War-Machine to join the TF-movie's for funnzies

 

Damn Sony and their rights to that character  

 

I can't see TF4 having the budget for any of those guys. If they did, I seem to recall the comics having a Captain Ersatz Tony Stark character. RDJ would be the obvious choice, for him.

And, who wouldn't want to see Scarlett Johansson in Circuit Breaker's gap filled outfit?

Unfortunately, I think Marvel might own the rights to both of those characters.

Of course, they could still get ScarJo for Marissa Faireborn.

 

Hell. To. The. No.

 

Nooooooooooooooooooooooo!THEY SHOULD STAY OUT OF TRANSFORMERS

 

Agreed, they're too good for these (now) crappy films.

 

Neither the actors or their characters would fit a transformers movie.

 

There is literally no chance for a mash up of these two