The whole Konohah storyline has been an exercise in cleaning up dumb little loose ends no ones cares about anymore (Saki and Wataru and Hamster, Aika's mystery fiance, Chiharu's secret maid life, the fate of "Video Koshien" and giving Izumi a pseudo-confession, ect. I didn't say they were
major loose ends.
It also seems to be building on Hayate's creeping realization girls actually like him and encouraging Hamster and Hina to make one last push. Konohah herself is totally irrelevant except as a catalyst and comic character.
To pull a slightly older example, remember Robot 8 randomly showing up during the beach episode? That whole little escapade was actually intended to be a final send off for him and the professor, his fate previously being somewhat...murky. Hata outright said so on his blog so I'm not making this up.
My point is that this is an entirely artificial and deliberate (and transparent) set-up, which is why you are surprised with recent developments and I am not. It's nothing more then a classic "Will they or won't they?" set up with the actual hook being "Oh that silly little girl, Hayate will never fall in love with her...or will he?"
It's no different then any shonen fight series ever starting off with "Oh you'll never beat
that guy, he's too strong."
As I said, it's not even rare.
Obviously the MC only expresses romantic interest in other girls that he will never end up with. It's completely safe to do so, locked down and secured by Hayate's butler status to make sure nothing ever comes of it.
Whereas the setup with Nagi and Hayate is a delicate one and Hata has to be much more cautious in keeping a careful balance so that the series can shoulder on consequence free.