I just can't see him as chaotic. He has a law: "stay alive and stay on top no matter what".
That just strikes me as neutral evil, that is to say, self-serving dialed up to 11. The reason he is not lawful evil is because he will always put himself first, and the reason he is not chaotic is because he is fully committed to his own freedom and survival.
I think we will get a redemption arc IF and only IF Astarion manages to forego either his desire for survival or freedom. That would naturally result in him dedicating himself to a purpose outside of himself. It would break his internal vicious cycle of wanting to be alive at all costs pushing him towards enslavement and enslavement pushing him towards wanting to be free.
This is very hard to write however and I'm afraid that Larian may not be able to handle it.
Or maybe they will surprise us and pull of something genius.
Or maybe he really is irredeemable.
I'm very hyped.