@Nicottia;;
Gale might be a demogorgon, who knows. I haven't looked into him that much yet

I am not going to be disappointed. I love the way it's set-up, because this makes me question Astarion. In a usual DnD party, set in Forgotten Realms world a vampire player character doesn't make much sense.
For a good character especially good cleric, once you know someone is a vampire you would likely want to get rid of them. And you can. They are evil by nature.
Somehow, Astarion is a sun-walker and if the dev interview is correct, he does lie. We can speculate whether it's correct or not, but it's
some proof. You can't just dismiss it. If the video isn't enough - there is an article about it as well -
here.
What if the demo, dream and other things that make Astarion's story about Cazador correct or true for you, is the exact reason they did the demo with Astarion, which wasn't completely from his POV? As you said, things change and this could have been exactly there, to help them sell this broken vampire guy that just want to get his revenge. He is acting like someone who is wounded. But that's what I think it is. Acting.
I've been around game development, this could be exactly what they are doing with it.
And I might be completely wrong. But no, I will not be disappointed. I really really like Astarion's character and how he behaves. The question is, if a vampire can really be genuine, or if this a plot that will completely change how we viewed the character, up until we played it or reached the conclussion with our own player character.
Anyways, whenever my crazy theories come true, even just parts of them I am very excited. My brain power can be used for more useful things later. This sparks joy right now and at least I am getting lots of lore info from wikis and handbooks

I am even getting some inspiration for my own DnD campaign.
This place is to discuss theories after all ^^