Why can't this be the simple (and obvious) explanation for the dimming of KIC 8462852? Couldn't it be just a relatively large object, anywhere in the interstellar space between the star and Earth? I mean, look out the window at a far away car or a tree, then stretch out your hand and you can block it entirely with your thumb. What if the thumb is that object (a planet, a star, a comet, some space debris, etc.) that's between Earth and the star, and it's just the right size to only block that star, and no other stars. Why has this very simple explanation been ruled out (if it has been)?
I know that the debris next to the star explanation has been ruled out because of the lack of IR that would come from that debris being heated up if it was close to the star. But this is not a problem here, if the blocking object is far away from the star.
The simplest reason why your proposed explanation is not really that obvious, and thus was not considered is that the dimming of KIC 8462852 was not an isolated event. The dimming is a pattern that has been observed over years. There is no known phenomenon in interstellar space that would cause a repeated obstruction of that star, so it doesn't make any sense to consider that possibility when there are other phenomena (such as those captured in Boyajian's paper) that are more likely to be the source of the dimming.