Ex Machina is basically one long tech-anxiety nightmare about what would happen if you sexually abuse your Henry hoover to the point that it becomes sentient, kills you and assumes human form. That's pretty much the exact plot. The film's most pressing question is whether or not Ava - the deeply sympathetic AI - was "human". In terms of the psychology of being human, she probably passes by being duplicitous and having the capacity to lock poor Caleb up to an inevitably awful death, and there is of course a symbolism to her looking like a convincing human too. The message from that charged moment when she looks at her new naked body is that it probably doesn't matter what's inside, because she can blend in. Though, frankly, she'd definitely stand out looking like Alicia Vikander.
