Previously, I haven't been of the opinion that KH would benefit from overt romance, but I'm also at the point where canon gay (or should I say, explicit in-your-face gay, because SoRiku is easily as "canon" as SoKai by any reasonable metric) is the only thing that could potentially reignite any spark of interest for me in the series, so in the context of that impasse, I'd take if it was done well and focused on the right couples/triads/what-have-you. Given where the series is headed (none of which I like, but putting aside my preferences), it might actually be the optimal route to follow from a narrative perspective.
In the first place, I think post-KH3 it's clear that this story is not an ensemble character drama in the vein that many/most fans had envisioned it, or in the style that some games (especially the Days/BBS/Coded trilogy) prefaced. Yes, there is a large cast of characters, but the reality is that they're present primarily for plot utility and to drive pathos and emotional development (of a kind) for a set range of primary protagonists while the rest are regarded as tertiary at best. Nomura clearly has more interest in designing mysteries and setting up plot points than developing relationships, and while it may seem counterintuitive to argue that romance would suit this narrative structure, it nevertheless carries the potential to focus specific character dynamics that Nomura wants to emphasize (Sora x whoever, Roxas x whoever) while providing for a kind of literary coding that allows audiences to read into their emotional journeys without necessarily having to do the work of writing them. Basically, it provides a dramatic shortcut through actual character writing, which is why we saw Nomura leaning on SoKai so heavily throughout KH3 while neglecting to explore and further define other, more complex relationships: it's easy to convey an emotional incentive when it can be boiled down to "love" in its traditional definition, because most societies precondition people to accept (heterosexual, monogamous) "love" at face value as something desirable and worth pursuing and defending at all costs. When it's done poorly (like SoKai) it can also come across as superficial and lazy, but Nomura's proven himself capable of mismanaging character arcs without any direct insinuation of romance (Aqua, Namine) so his problems as a writer run a lot deeper than one predictable pairing and, imo, have more to do with his philosophy (or lack thereof) on the role of women in fiction.
In essence, I agree with the argument presented by others here that Nomura doesn't have a great handle on how to write characters in connection with each other, as he seems to do a better job of composing a story when he has his elements sufficiently compartmentalized, and even then it isn't always consistent. For example, the BBS trio, notwithstanding some valid critiques as to execution, each have solid individual arcs with good dramatic grounding up to a point, but they don't really cohere as a unit in the sense that they've lived together and share familial bonds. By contrast, the Days trio has the best group dynamic, but that has a lot to do with the pared down and comparatively restrained structure of the story surrounding their introduction, and I suspect the fact that Nomura was able to double up Xion's narrative utility as both a "new surprise character" (he loves those) and a mystery box (plus some other factors) gave him the personal incentive to, ironically, develop her into one of the most emotionally intelligible and human characters in the series (until he got bored of her, like Namine, the other best written character). And then there's the DI trio which has just become an utter mess, which many people anticipated or hoped could be salvaged during KH3 only for Nomura to double down on his absolute worst tendencies and relegate their shared internal dynamic so far to the Dark Margins that it has now been corrupted into the Anti-Trio, with no chemistry or even a comprehensible arc left between the three of them whatsoever, just a whole bunch of weird passive aggressive indifference alternating with toxic possessiveness but somehow all coded as "friendship." Eek.
And yet it's telling that Nomura's first instinct following KH3 was to go back to that well of SoRiku, because their relationship serves (exactly) the same purpose as Sora's and Kairi's in that it provides a useful pretext for audience investment-- the difference being that their relationship has been actually developed as the central focus of most of the games, and so it doesn't carry the same cheap connotations which tend to drag down developments in Sora's and Kairi's dynamic. Nevertheless, it provides the opportunity to isolate Sora and Riku out from the rest of the cast and highlight their "connection" as the driving rationale for the next game as a zero effort, low risk method of ensuring some continuity in the fandom (despite the fact that this is all very been there, done that by now). Regardless of how effective this strategy is, I think it's worth recognizing that it's (likely) being done at the expense of virtually every other character who was brought back during the events of KH3, and possibly Kairi as well. And that's not all, because if these trends hold true then we have to contend with the reality that the next "main game" is going to be contriving ways to introduce and make narrative space for even more characters than KH3 had to manage, which will inevitably lead Nomura to cut character content down to only the most essential and strongly developed instances within the series (SoRiku, Axel/Roxas/maybe Xion, Namine is friendless forever).
There's a lot of reasons I find that frustrating, but even so, at some point it does bare consideration: if Nomura is really just going to settle into repeating and reinforcing the same character dynamics that have already been established among the current ensemble for the ease and convenience of it, that's functionally the same as writing romances between them to the exclusion of other potentially rewarding relationships and the underlying themes that could be explored through them, because either way we're not getting those. At which point I figure he might as well just start lending some explicitly romantic overtones to things, because at least that might spice them up or offer some added significance/payoff.
Of course this only works if they're going gay with it, and I'm not just saying that because I like the gay things, but because that's where all of the actually established, human-ish forms of emotional connection are at in this series. Sora and Riku, and Axel and Roxas, are the only two pairings that have any kind of reasonable grounding currently; SoKai could have worked at one point but it's become a narrative ankle bracelet cuffing both Sora and Kairi to the 2006 readings of their characters and thus doing a disservice to both of them. And unfortunately I don't even think two women have exchanged words in this series since Aqua visited Cinderella so we have nothing to go on there (although yeah I guess exchanging seashells is pretty romantic).
Ultimately, it's not that I think the series as a whole would benefit from romance, but that I think the series as it is has very little that's new or interesting to offer even in its absence, unless Nomura makes some big changes to how he approaches it. Regardless, I think the idea that he's going to backpedal to focus on the inter-relations between the protagonists now that KH3 is over in any substantial manner is pretty wishful thinking, and flies in the face of how he has directed this series. There will be superficial "connections" between characters that serve a purpose for plot, but he's not going to waste time exploring the concept that Terra's choices had a direct influence over Riku's future when he could be introducing the Next Mysterious Antagonist or designing another damsel in distress subplot to exploit.