[Merskelly Metalien]

Discounting Dyson spheres, or other alien interference, what is the going theory for the dimming of Boyajian's star?

Well, the star is hungry. :[ Right? So what do stars do when they're hungry? They eat what's around, so like, planets and stuff. So you know how, when you eat, and you get full, you feel like sleeping after? Same with stars. x} They get sleepy and dim a bit.
The answer is, it's eatin' stuff around it. :]