In FO3/NV you couldnt bring companions to or from DLC locations, this changed in Skyrim. Do you think the devs will change this trend in FO4? Also as a side note we could get additional companions to bring back to boston with us from DLC!

We don't know yet but there were mods to fix that

I think F4 will be like Skyrim when it comes companions in DLC areas. I also think that the companions will be just as worthless as those in Skyrim, hehe.

Sneaking with Mjoll The Lioness by your side? "Shut the [BIIIIB] up, Mjoll!"

Edit: Sidenote; aren't Hemeras Mora Realm and The Soul Cairn, areas companions can't enter?

Probably depends on the story of the dlc, if they want to showcase plot important companions (like in New vegas) then they probably shouldn't let you bring your pet and murder buddy. If its just like skyrim where dlc areas are just another map to explore then i don't see why they wouldn't. Hopefully companions recognize when they go into new areas though, or give you a reason why they wouldn't want to travel to whatever hell hole the dlc takes place in.