With a lot of this: (a) it will never, ever go beyond subtext as long as the show goes on. So you're only discussing what romance will they hint at, and that's the romance of the show and (b) they don't always have those plotted out. They hint at one or the other and see how fans react. When New Game started, they hinted at a triangle of Rin/Kou/Aoba all the time. In fact, Aoba and Kou staring into each other's eyes completely romantically was an anime splash intro. But when Hifumi started opening up to Aoba, apparently the fans liked it, or the creators decided it fit better. Nowadays, for the most part, the Aoba/Kou subtext is on the back-burner. Nowadays, the subtext couples seem to be Kou/Rin - with Rin's rival being, not Aoba, but Kou's job that she's basically married to; Hifumi/Aoba which is, despite Aoba's cute feminine little girl appearance, pretty much a classic neko/tachi relationship; Umiko/Nene which is a little less romantic and kind of a sempai/kouhai subtext; the spares are hinted at pairing off or perhaps getting something with the new girls.