well I mean the general origin of exo's was they started out at constuction suits for building the station. Ya know protect the workers from the vacuum of space and any debris as well as for heavy lifting inside (after they had gravity). 

That's pretty much all the official lore I had for them. They were chosen to be remade into exploration and combat exo's for since they would be easy to retrofit and the station only needed 1 or 2 on board for repairs.

So go wild, and then we'll see.