[Zanibas]

Okay, so from first glance, the final Kyousuke/Kirino interaction doesn't seem THAT deep, with kicks and all tsun tsun, but upon reexamination...

Spoiler for Analysis of Final Scene:

Take for example the first shower scene with the panties. Kirino is genuinely annoyed because she wants to hurry and shower for her beloved imouto. So when Kyousuke interrupts her to announce the panty drop, she shows her annoyance.

Jump to the end scene, where we're in an almost identical scenario. Kyousuke "oi"s her again to tell her goodnight. Her reaction from the oi? Not irritated, but actually surprised.

Now of course this may just be how every episode ends, but I believe something can be read from this. Kirino, having played through the "taste of own medicine" eroge, decides to see her brother's reaction by PURPOSEFULLY acting annoyed. Note how the two options she was given in the eroge were either "Tolerate it" or "I've had enough!". Could be that she wanted to see if Kyousuke would make the same decision too and tolerate it.

Anyways, that's my wild theory, go ahead and bash it all you want :P.