I can see that, I just don't like it. However, there was one idea someone had elsewhere where after Micah is thrown at the screen, the demon let's go of Katie, and she realizes that Micah is dead. She rushes to the body and starts crying or w/e and then like we see earlier in the movie, the demon starts to pull Katie back towards the attic. That ending is incredibly like Quarantine/REC, but I feel that the scene earlier was creepy as fuck and would've had more of a "final scare".
Another one I read was more simple. Instead of Katie being all demon and shit and sniffing Micah at the end, then lunging at the camera or whatever, she simply walks over to it, with that creepy smile on her face and just turns the camera off. That would've been more effective than the theatrical ending imo.
I really just don't like the idea of her slitting her throat. However, the one ending where she sits there for several days is pretty creepy, it's just once the cops come in kind of ruins it because they shoot her so fast