I'd bet a shiny new nickel that this chapter and the last chapter will show up in the next tank before the chapter where they have sex. The author's afterword in Vol 4 indicates that there will be another volume, but there are only two stories left in the original run: Yamada goes to take her exam, and Yamada and Kase do the big nasty for the first time. Which is (A) not a lot of material for a tank; and (B) something you'd want as the climax of a tank, rather than a story you run into 1/3rd of the way through.
As far as what's yet to be published in tank format, there's also Rival and Kase-san, Christmas and Kase-san, and the recent Going to Tokyo and Kase-san. And maybe if they really need more material, the Chocolate and Kase-san doujin.