I think the idea of a Like a Dragon character getting in next is something people might be overselling at this point in time. Every time we've gotten a character by and large associated with rival platforms, there's always been some sort of special circumstance that got them in.
Snake was a direct request from Hideo Kojima himself, and probably wouldn't have been in Brawl if Kojima wasn't insistent with wanting him in.
Cloud wasn't the immediate decision for a Final Fantasy character, and Nomura had suggested the protagonists from V and VI, which were more closely Nintendo-associated, but Cloud was ultimately chosen because Sakurai felt that since they were going to add a Final Fantasy character either way, it might as well be the franchise's most popular character, even if his game was nonexistent on Nintendo platforms at the time.
Richter more or less got in because of being able to be turned into an Echo for Simon, which also let the devteam merge the two Belmonts' techniques into one moveset as a result.
Joker's home game is explicitly a game that Sakurai really liked and had influenced certain aspects of Ultimate, particularly its HUD. Joker getting in was essentially the reverse of Snake's situation, where it was Sakurai who really wanted the character in Smash instead of the other party involved.
Sephiroth is a case where we don't know the entire story, but it's easy to infer that he was more or less part of whatever deal Square wanted in order for Ultimate to get more FFVII content in. If the music and Spirits that came with his Challenger Pack were in the base game with Cloud, I'd imagine Sephiroth wouldn't have been seriously considered by the devs, at least not for Ultimate.
Kazuya is also a character where we don't know the exact nitty-gritty of why he's in, but as with Sephiroth, it's easy to infer that his inclusion was likely a mix of Sora ltd. and Bandai-Namco being closely-involved, and Sakurai and Harada being rather acquainted with each other on a personal level like with the situation revolving Snake and Kojima. Like with Sephiroth, had the circumstances been different (say, if development of Smash was still with HAL Labs instead of Bamco), Kazuya would likely have remained a pipe-dream pick IMO.
While Kiryu's first two games did see a re-release on the Wii U, the collection was a financial failure, and to this day, no other Like a Dragon game has seen a release or even a promise for Nintendo systems, even after Nagoshi stepped down and left SEGA. Combine that with a statement by the team that Nagoshi didn't want to see Kiryu in a fighting game because he can't imagine him fighting female characters, and I feel that Kiryu is in a much tougher spot compared to the likes of Snake and Kazuya. Sakurai's devteam doesn't have the closeness with Sega's non-Atlus alumni like they did with Bandai-Namco, and even if Nagoshi hadn't left the company, it didn't seem like he was in a rush to want Sakurai or any of the other Smash devs to add Kiryu or any of the other characters to Ultimate. The main reason why I don't say Kiryu's chances are zero, however, is because we obviously don't know Sakurai's personal thoughts on the Like a Dragon franchise. We don't know if he's passionate enough about the series to want to include a character from it when the opportunity arises, or if he doesn't have any real strong feelings about it.
In a nutshell, I can't imagine Kiryu or any of the other characters being the #1 priority for the next Sega character in Smash unless Sakurai is incredibly passionate about the series like he was with Persona 5.