Eventually they may get to this, the game doesn't have enough content to support this yet though.
They do charge you extra battle points for heroes/villains outside of that battlefield's era and they do have some comic relief when you summon one outside his era.
I personally don't mind being able to summon who I want. I personally only have a handful of heroes that i feel are worth playing anyway.
I personally go with a wookie enforcer over any light side hero (though Rey's wall hack support is legit) and only think Boba Fett and Bossk are worth my battlepoints on the dark side.
IMO there are a lot of bugs to fix and other adjustments they need to make before they worry about the small details.
Though of course I'd love to see more heroes released.
