>>3144029Kirino thinks imoutos are cute, which they obviously are. Whether she likes watching them get dicked or not doesn't mean she likes them being yuri'd, and that doesn't mean she herself would want to yuri either.
It doesn't matter that Ruri's line is specific; when they go into the whole feeling her breasts part she says that she can't blame him and that she's thinking of things too. I know that they doesn't specify anything lewd from her side and she would deny it up and down if asked, but it's impossible to believe a girl who just got her first boyfriend that she really, really likes (and wrote a whole damn journal about) isn't at least thinking about kissing, if not more. Regardless, if they were alone and it was romance time, she almost certainly would do whatever he asked her to, within reason. Probably just touching since thats usually what follows kissing but thats still more than what you'd expect with the air she puts on. I doubt she would be ok with sex after a first date or something like that, but if they had been together for a while and had already gone sexual, I could see her lewding Kirino if it was at Kyousuke's request. The three's relationship is far from normal to say the least.
Remember, the only reason they stopped the hand holding is because she physically wasn't able to handle it, and things wouldn't stay that way forever if they had remained a couple. Eventually she would've gotten used to it and everything that comes afterwards without being embarrassed. The only reason I even see this as a possibility is because Kyousuke actually does love them both, and they both do love Kyousuke and they are best friends who understand how the other feels about him.