@b-no I may not be a Nino fan, but if I had to represent my thoughts of who to ship between Nino and Ichika, that "shipping ended" picture would 100% represent my thought. Nino may have been a detestable character before, and while I may not be fond of her forward advances, in the least they seem to make sense to her character. I don't agree with people who say her development thus far has been the best "bad-to-good" transition, but as time has gone, I will say that in the least, she is consistent which I can appreciate in a properly formed individual/character.
On the other end, as you mention, Ichika has been... "lame"? I'd rather say that while her motives are honourable, the actions taken or the results of interactions with her have been satisfactory at best. Before, she was okay onee-san, but it was much too typical to have her be "I tease, but in truth I'm shy." People say that she's going back to her who she was, all brash and mischievous in ways, and sure, whatever floats their boat. But that in itself is not proper development, just backpedalling. Plus, as
@Misticsan mentioned, Ichika's action don't compare to Nino: Nino has been selfish for attention, which has certainly caused some roadblocks for the sisters, but Ichika's attempts have been an outright effort to sabotage the other's efforts in order to attain that attention... and I thought Nino was too crass to see her in a better light, but nope, here we have Ichika.
While I may be taking this next point too seriously, and may have mentioned it before, I am tired of people who say "X is sexy/cute" or "Itsuki is first girl, so she win" (yes, I am being specific for Itsuki). While it is true any story can follow a formula, it feels dull to believe in such surface level elements when liking a character or foreseeing plot development. Certainly, it isn't convincing when a good too many romcoms does result in "first girl wins" or "sexy fare well in the race," but to me, when looking at fellow fans, I am disappointed by such shallow reasoning. One commentor, princeofcups, stated if people are just making statements to be cool or for their waifu, and sure some people do pick on such simple thoughts. I don't like it... but in the least, they are wishing for what they believe is the best the series can offer. I am not cool with their latter statement of "Does anyone REALLY not understand that Itsuki is the bride?" because, let's be honest, no one knows who is going to win. To state as if it's fact is pretentious, on top of it being boring, and anyone who says it like such without a "this is only my thought," is much more irredeemable than those who just light-hearted support their waifu. If the series does end with Itsuki as the bride, sure okay, gj author, not fascinating; we are free to believe that a series will be better and not so one-tracked due to tropes/cliches. We are free to expect better, because really, the girl we root for should deserve that.
Last but not least... Itsuki seems to be doing... "better"? I will admit, I am just as confused as some individuals as to where she lies in all the secrets and romance. With all the show of a platonic relationship and no significant (or at least memorable) character arc, I don't think her "I'll eventually tell you some day..." was meant to be anything romantic when looking at the previous page. She was talking about her aspirations and what has probably changed among her sisters. Of course, I could be wrong, and this may be a hint that she is Reina (past or the present), but to me, she hasn't been on the romantic radar as others have also deduced. Similar to Yotsuba, she's been more of a good friend that Fuutaro can chatter with, although I'd reckon it is just because there hasn't been a reason to push him away aside from the distrust at the start of the series (and unlike Yotsuba, seems to lack any apparent ulterior motive than being a good-natured friend, not that Yotsuba has any "ill-intended" motives).