I hated the Achiga spin-off from the beginning; their treatment of classic "shounen protagonist" sort made no sense in building up Shiraitodai as the final boss, which in turn makes no sense for the progression of the overall manga which for the previous 17 years had always been about how outrageous Teru and her school was supposed to be - but much of what was shown was in the Achiga manga, so I could buy into a "protagonist extra bonus" explanation. Having it spill over in the main series is worrisome though.
Of course, there was always going to be the conundrum of Saki not actually playing Teru. So it might very well be that this finale will ultimate serve an entirely different purpose than anyone could originally have guessed. Well. As others have pointed out, sometime by 2060 we'll probably know.