What makes you think Abrams would even direct it? I doubt he would. He will only produce it at most.
My question is this. How do you take the experience of Portal and boil it down to a two-hour movie and make it compelling for a narrative experience.
I think the Portal games are very interesting with interesting characters and narratives. However, they aren't traditional linear narratives. Plus there's a lot of weirdness I don't think would play well with moviegoers.
Now I could be wrong about Assassin's Creed. But I'm sort of disheartened with how they've established that most of the movie takes place in present day. The whole appeal of Assassin's Creed is you are experience the memories of your ancestor as an Assassin in some crucial period in history. You are getting to actually relive those memories in the past. You are more than just a fly on the wall to historic events, you have become a part of them. You get to meet and interact with historical features. You become a badass assassin with cool abilities. The Assassin is the player getting agency in the game. You're transported back to your past.
I mean who wouldn't want to do that? Get hooked up to a device and get to relive some past events as an ancestor. But you aren't a random bystander. You are a true blue assassin who is part of an ancient war that has lasted as long as recorded history between two warring factions. That's a cool concept. No one cares or gives a crud about the present day storylines in Assassin's Creed. Ubisoft definitely doesn't. They barely pay attention to present day plots a tall.