I complained about the ending to Paranormal Activity (it seems to be referred to on YouTube, at least, as the 'CGI-demon face' ending) and mentioned the existence of at least two other endings. This, apparently, is one of them. (Though it still has the creepy, but dumb, evil-smile right at the beginning of the clip.)
It's better than the theatrical ending, though not by much. The complaint that it's anti-climactic and drawn-out much too long are well-deserved, though Katie's death is legitimately surprising. (Couldn't it have simply ended with her rocking and/or leaving? Something subtler, and more in keeping with the subtly creepiness of the film on the whole?) And it still suffers from that 'realism' problem. If the theatrical ending is bad because it's horribly 'unrealistic', it is also bad because there's no way it ever would have escaped police custody, much less been distributed as a movie - and that latter complaint applies just as readily to this ending.
Blair Witch, at least, could plausibly be released because it would have been impossible to prove whether the film was a hoax because the filmmakers corpses were never recovered and none of the three was obviously implicated in the murder of the others. But Micah and Katie's bodies would be all too real.
I still haven't been able to find the third ending, which actually sounds like it would be the best one. (Though, to be fair, based on the description I was expecting this one to be something else entirely.)