Look at all the loading screens...all of it is just the original companions...I doubt they will add more.
The loading screens aren't necessarily indicative of anything. There's several composited images with the available characters together in different compositions as well as in stand alone images. Each piece of character art is it's own piece (you can see them by themselves in character bios). So it would be easy for them to change up the composition with additional characters or make loading/splash screens with different companion groupings based on alignment. Since no other characters are announced as of yet, it doesn't make sense for them to leave spots open where they would be.
Photoshopping is easy.
