One thing I have realised and it might be wrong but you never know,
Is that some companions might change their alignment depending on the path your PC takes, (obviously theres some approval and disapproval involved)
But speaking specifically about Astarion and they way he reacts to your choices in both versions of the party has me wondering about how much the PC will effect the origin characters!
For instance
if you side with the druids, Astarion states that he could get used to the idea of being a "hero" (if my memory serves me correctly!
And then if you side with the goblins he relishes in the idea of murdering some more
It just has me thinking, if that is the case then it would be interesting to see how much you can either corrupt or "redeem" the companions!