Well of course I am going to start a discussion on if the Enclave will be making a return, So I have some evidence that supports this first off is the F3 Eyebot that you see in the trailer my best guess is that it belongs to the Enclave as they are currently the only faction that is known to use them. second the X-01 Mark II power armor it has a lot of simularitys to the APA Mark I, there is also aparently armor in the fallout shelter game called X-01 Mark IV, and finally Vertibirds. So my speculation is that the Enlcave will be in Fallout 4 but as a minor faction

The Vertibirds look like they belong to the Brhtehood, but let's not get to hasty here. Why the power armor looks like the old version, I don't know. I'd rather have both, but that remains to be seen. The Eyebot is interesting though. It could be that The Enclave is just a small group trying to persuade people to help rebuild America, and that this Enclave doesn't care about background mutations (ghouls and muties will always be bad though) only to get more people to join their cause.