Although the Karami Zakari manga wasn't entirely written by Kastura Airi, the final chapter of Karami had a plot twist, so with that in mind, the final chapter of "Grapara" might also have an unexpected twist.
I can only wonder what twist it's gonna be. If at all.
The only thing I can think of is something that has to do with the parallels between Sakura and Shinobu despite their separation. It's noted that they seem to be going through similar scenarios for their respective careers.
Yet so far Shinobu is the only one being tested when it comes to doing a lewd scene, with Fumi basically going against what he planned out. I wanna say she's not doing it out of spite because that just doesn't make sense but rather to just prove she's willing to support Shinobu however she can.
Sakura however, from what we see, seems to be doing fine for now. Granted all we see is just her removing her shirt and showing her bra. I would not be surprised if this next chapter shows more how things are from her end. Her own test on if she can go through with it.
But again it's possibly the final chapter so.. who knows what direction this goes.