Although it is my favorite Star Trek series, the older I get the more I realize that DS9 is full of missed opportunities. To be fair, there is a lot more awareness of how broad the queer and gender spectrums are today than in the 90's, but I definitely feel like if they made the show today it couldn't help but be more representative. Here's my take, by character:
Ben Sisko - Not a great start for my case, because he's the character I would change the least. It's not that I think he has specifically het energy as much as his romance arc is basically perfect for the character. Sisko has a lot going on: he's a dad, a commander, an administrator, a freaking Messiah. He's still mourning the wife he lost in a violent tragedy. Sex and romance are secondary concerns for him, so it fits that he has so few entanglements and ends up in a happy domesticity with Cassidy. If I changed one thing, I'd have his mirror universe double be sleeping with Bashir instead of Jadzia. It makes as much sense and is funnier.
Kira Nerys - Gaining a little momentum here. There's a tendency in the fandom to code her as a butch lesbian, which is understandable and fits the character. I do think she's bi, though, and definitely a serial monagamist. She's also the first link in the polycule - more about that later.
Odo - This is kind of my Big Deal character. Odo's love for Nerys is a series-long plot point, and he has a couple of other dalliances along the way, but I would do away with all of that and make Odo, at the very least, ace. Possibly aro, but I'm willing to discuss that aspect. But consider: Odo is an entirely different kind of life form. His default state is a gelatinous ooze. He "grew up" in a lab. Not only does he not have hormones or any sort of mating instinct, he doesn't even have the social programming to make it feel like a priority. The idea of sex should be as weird and gross and alien to him as eating or drinking. Something solids are driven to by their biology but which holds no appeal to him.
Julian Bashir: Bashir is absolutely that bi person who didn't now he was bi until well into adulthood. Maybe he grew up in a very heteronormative environment, but whatever the reason it just...didn't occur to him. And hey, he's good looking and smart and reasonably charming, so it's not like there weren't girls around. He had male friends but never formed a romantic or sexual connection. Until DS9. Suddenly he's being seduced by a scary/sexy Cardassian and simultaneously finds himself very drawn to and eager for the approval of an older Irishman. He's also spending a lot of time with Jadzia, who in addition to having a certain amount of masc energy herself is the dangerous combination of perceptive and completely lacking in filters. When she casually points out that he's obviously into both Garak and O'Brien, it changes his whole world. He's the second link in the polycule.
Jadzia Dax - the most explicitly queer character on the show. Jadzia is omni and poly, no two ways about it. She and Nerys have a fwb thing going on, which causes occasional tension because Nerys (as stated above) is super into monogamy but she understands that's not Jadzia's bag, but aside from that she's completely a free agent and remains apart from the polycule. Or maybe she kind of dips in and out of it? I do like her and Worf together, but more on that later.
Miles O'Brien - Like Bashir, O'Brien came out to himself late in life. Much later, in his case. He's a no nonsense, no drama kind of man. I think of him as very "meat and potatoes:" it's not that he was raised in an environment that demonized queerness, it just never occurred to him that he might be queer. When he fell in love with Keiko, he was happy to get married and have kids and let that be the end of it. Then he got to the floating love shack that is DS9. First, there was the doctor. Half his age, utterly not his type, and already on his way to a somethingship with the Cardassian spy, and yet. It takes a while for him to come to terms with what's happening, mostly because he knows he's in love with Keiko and the idea of polyamory isn't something he's accustomed to. Push comes to shove when the pregnant Nerys moves into their quarters and the pair of them begin to develop feelings for each other. Finally, he makes a complete confession to Keiko, confused and frightened, only for her to basically shrug it off and ask if he wants to invite Bashir and Nerys to form a polycule with them. Some explaining and reading later, he agrees, and the core of the station's polycule comes into being.
Quark: Hoo boy. My first instinct is to tread very carefully with Quark, because Ferengi culture as portrayed in DS9 is suuuuper toxic even though it has a definite progressive arc. But there's something about Quark, and about all the Ferengi males we see, that I just realized: they're all subs. Every one of them goes absolutely gaga anytime a dominant woman enters the room. From Ishka to Leeta to Jadzia and Mirror Ezri and beyond, these dudes lose their minds for an assertive, powerful woman. And I think that's an interesting angle to take. It adds a bit of kink to the show overall and throws an interesting curve into examinations of Ferengi culture and how it begins to shift. Why is the Grand Nagus implementing all these reforms, you ask? Because his dommy mommy Ishka told him to. Also with Quark I think there's an opportunity to explore sexuality via the season 2 episode "Rules of Acquisition." Quark's super tight bud Pel, who is also really great at business, kissed him! And confessed his love! But, twist, Pel is a female! (spoilers, I guess) And now Quark is completely lost because he doesn't know how he feels about the whole situation, and what that means for his sexuality as a whole.
Jake: He's a kid. I'm just not going to go there.
Okay, look: he comes of age over the course of the show. Maybe we can show him dating various genders and species just to see what he likes. Maybe some masc or androgyne or even hermaphroditic alien asks him out and he's like "huh, sure." Also: mommy issues. He likes older women. It's a thing.
Worf: I feel like Worf is a big ole bundle of insecurities, false assumptions, and cultural programming. At heart, he's a romantic. He's the product of two sets of loving, committed parents and he's made that his goal. He wants the love story that ends with marriage and happily ever after. Unfortunately, it leads him to love bombing and jumping way too deep into relationships way too soon. His time dating Deanna helped a little with that, but it's still a problem. On top of that, he's obsessed with being the perfect, ideal Klingon warrior. So obsessed that it makes him kind of a loser nerd among the Klingons, who generally aren't nearly as hyperfocused on honor and glory and all that jazz. He was so young when he was removed from Klingon culture that he only has vague memories and whatever Federation culture believes to be true. I think Worf may be the only actual heterosexual on the crew, or if not he's so deeply closeted that even four seasons on the Queer Love Boat isn't going to get him out. He does fall in love with Jadzia, but can't make it work because unlike Nerys he just can't acclimate to her poly lifestyle.
Garak: Have you read A Stitch In Time? Read it. Garak is bi and sapiosexual.
Ok. At this point I could spiral into going through every secondary character, but I've made my point and set the foundation for what I really wanted to describe: The Polycule.
It starts with Keiko O'Brien, not so much as an instigator but as a catalyst. Keiko is bi and at least familiar with polyamory. She hasn't done anything about it since we met her because she's in love with Miles, and he's always presented as hetero and monogamous. Then one day he comes to her all torn up and confused, feeling like he's already cheated on her emotionally by having all these feelings about Nerys and Julian. And Keiko just smiles gently and explains to him that love and sex and relationships are so much more complicated than he's always thought about them, and if they need to make room in their marriage for his needs they can at least have a conversation about it. So they do. Several, long conversations. And by the time Kira Yoshi is born they've decided to approach Nerys. She's surprised, but has been quietly struggling with her own growing feelings for both O'Briens. And being part of a polycule is much more up her alley than the casual fwb she has with Jadzia. They go official, and with a little coaxing Miles approaches Julian as well. Julian takes much less convincing and soon they are a quartet (note - not foursome). Julian, emboldened and enlightened, then approaches Garak and they begin to date. So we end up with: Miles married to Keiko, dating Nerys and Julian. Keiko, married to miles, dating Nerys and fwb with Jadzia. Nerys, dating Keiko and fwb with Jadzia. Julian, dating Miles and Garak. Jadzia, fwb with Nerys and Keiko, occasionally domming Quark and sleeping with Worf. Odo harrumphing over all of it and Sisko good naturedly rolling his eyes and quietly praying it doesn't all implode in some drama chain reaction that would destroy the station more thoroughly than anything the Dominion ever tried.