According to the canceled Fallout d20, the Eastern Brotherhood power armor was based on a commercial variant that was available briefly before the Great War.
I would redo the sprite of the Power Armor to make it more retro. Not that there is anything technically wrong with the sprite, it's a great piece of art. It's just that it is a bit out of place in the Fallout Universe. But bear in mind that we had to design it over a year ago and Interplay approved everything we did. - Tony Oakden, producer of FOT (Freelancer interview)
Why does the Power armor look so different from previous models? - Different group of BOS, different technology. - Ed Orman (Freelancer news)