You can feel it in this chapter the most (right after the no build-up, jump straight to the final boss fight with Majin arc), that the Editorial department probably had enough and prompted the series to be wrapped up in the next volume.
Given the long-winded way we managed to arrive at the point of the story where Hanako opens her eyes, we also got closure, for the most part, on Kanon's end. Chapters usually weren't this packed with plot from what I recall.
I'm very skeptical about a 4th installment being possible, my assumption would be the whole - Mahjong never makes anyone happy smh - thing to be trumped by Kiriya facing off against Majin, beating him - telling him to return to his wife, and never look back at the summit (Kiriya himself) again. I guess we'd get a teenage Koume looking for her Dad as the final story arc / 4th installment.
I'm honestly leaning more towards this entire series getting wrapped up in short fashion. My best guess is that the long-lasting readership had enough of changing up the main MC from Kiriya to An. Here's to hoping it at least doesn't end in a train wreck. :s