Going nuts with this new idea...
So, assuming that Daisuke and the others aren't dead in Tri and that there's a Big Bad out there that everyone will converge to fight, I've got this thought about Daisuke and his Crest of Miracles... And the idea that he doesn't believe in miracles at all. I know I've mentioned this for another story idea, but this one will go along with Daisuke being missing after some sort of mission alongside Miyako, Iori, and Ken. In this case, during the final battle things aren't going well for the Chosen. When things start looking especially grim, Daisuke will dig deep into his own power, but because of his disbelief he will not have any sort of control over it. Lacking focus, when trying to bring the power of Miracles to bear, he will instead detonate it, quite literally erasing the entirety of the Digimon World.
A shield will form around Hikari when this happens, not due to her own powers, but because even with no control at all, Daisuke will still instinctively protect Hikari, even from his own power. All that is left is Hikari, Gennai, and a few select Digimon in a disconnected partition, utterly blank and unable to reconnect back to the Human World. Gennai will explain to Hikari about realizing that the Chosen would be unable to win and setting up this space in case anything could be done to circumvent the coming tragedy. Gennai explains about Daisuke, Iori, and Miyako receiving their crests, as well as Ken recovering his crest, but Daisuke being the only one unable to activate the crest. He'll then describe discovering that when in the digital space, human beings are connected to themselves, both past and future, and Gennai used that connection to discover just when Daisuke stopped believing in miracles: right after the defeat of BelialVamdemon.
This surprises Hikari, but then she recalls what Daisuke was like at that point, and comes to realize that she hadn't treated him very well that year they fought together, despite him being her best friend. She was off-put by his affections for her, and she reacted by turning away, to someone that she knew would set off his jealousy. It's at this point that Gennai tells her that they might be able to send her mind, no, her very being back into herself at any point that she was in the Digimon World. Hikari accepts and they get to work. Gennai orders her to enter her body right at the final battle with BelialVamdemon, but she has already decided to go back further, to right before she left the Digimon World after her first adventure. She has a plan!
Going back is disorienting, and very sad because she arrived in her body right after gifting her whistle to Tailmon. She gets through the tearful goodbye and the Chosen return to their world via the tram car. Hikari gets reacquainted with being back in time, then asks Taichi to have a talk with Daisuke, who at this point is her friend, and really almost her best friend. Basically, she wants Taichi to talk with Daisuke and get him to realize that he doesn't need to act out to get her attention; he just needs to be himself. After they talk, Hikari decides to tell him all about Digimon and her adventure and everything.
Daisuke will mature a bit from these conversations, and he and Hikari will grow closer because of it. I'm toying with the idea of Daisuke getting a Digivice early and joining Ken and Ryo on their adventure, but I'm not sure how to go about it. And I'm not sure if I wouldn't be stepping on toes by doing that.
Anyways, that's as far as I have it thought out. I'm not going directly for the Daikari 'ship, but it'll be there eventually. Daisuke toning things down and being himself will allow Hikari to grow more comfortable with him, and that in turn will allow her to entertain thoughts of being together with him. Perhaps not while they're still 11, but let's just say that Daisuke will not be given a chance to lose his belief in miracles...