Yuka and Eri appearing in that flashforward makes them appear as if they're important. In most of these games, side characters' routes aren't required for the best or harem endings, they're usually added filler at the end with stuff like "so and so was there too." And important love interests usually equals main love interests. And if that flashforward is basically the "best/harem" ending then yeah.
And it'd depend on if that character's story being focused on affects the ENTIRE game. If the post he made a while ago said something like "I'm holding OFF on their stories for a while." Then it'd be fine. But instead it pretty much said that he's making them side characters. So less screen time, less development, pretty much less everything.
It wouldn't make Harry a main LI but it could very well mean he's now a main character. (hopefully my memory is correct) He's that blonde guy who's basically the MC's best friend right? Judging from some hints and tells, he pretty much already IS an important character too.