In my view, Larian has rather clearly
said that Early Access would be Act 1 and capped at level 4. I don't know if they explicitly made further statement saying that "no, no, no, there won't be more", but then again there's no reason to believe that they'll change their mind on this plan.
The FAQ says that there will likely be new races and classes added to EA. It doesn't say so for levels and story. And in a recent
interview, they said that EA is just for testing systems. So additional story content is pretty clearly out.
Granted, additional levels are more systems, or rather technical content, and not story content. But I think Larian's intent for EA is solely to see how people engage with and react to more fundamental systems. Whereas opening level 5 would be more for balancing purposes. So, for what it's worth, I greatly doubt they'll add level 5.
I'm not saying it wouldn't be valuable. In fact, I'd kind of want to know that many people tried level 5. In a
GDC talk about the making of D:OS 2, Swen explained that their EA, which was also limited to Act 1, and their internal testing didn't allow them to see some problems with the progression-and-difficulty curves. BG3's EA is similarly limited in scope, so I hope their internal testing got better. Admittedly, the D:OS 2 problems were perhaps more about characters having progressed too much in level at some points of the story. But as level 5 sounds to be really a big deal in terms of power, it will affect the face of combat. Anyway.
@Tuco : the fact that level 4 (and level 3) is reached quickly might be precisely the goal in Early Access. Level 3 is when every class has chosen their subclass and we have access to all the EA spells and abilities. For playtesting purpose, I like it that I can reach this point in 1h-2h, if I don't have a save already. The progression curves can easily be adjusted, either by tweaking the XP-to-next-level requirements or the XP rewards. And it would be a lot more sensible for Larian to leave those adjustments to the very end, when all the XP-yielding content is ready. Hopefully this time they'll do it better than for the release of D:OS 2.