I’ll be quite surprised if anything results in this without the cliche drama of an outsider getting involved to break the status quo. I feel like Kasumi is smart enough to not need that sort of thing to honestly resolve this sort of long overdue question from Sakurako’s side nor has she seemed like the jealous type to be affected by that sort of thing anyways.
At the same time, we did for the first time see Kasumi actually acknowledge and boldly state the fact she is Sakurako’s #1, so perhaps she does need to be reminded that in their long standing constant pace and world, things can change even in ways she doesn’t want them to. Maybe we’ll start to see Sakurako wean off of Kasumi and start to question if just being with Kasumi but not being with Kasumi is something she actually wants for the rest of her life bc by now it has been close to 10 years for them.