Been playing through 0 lately and I'd love to see this happen; I even have a Kiryu Brawler Mii on Ultimate right now, lol.
Honestly, a super aggressive, rushdown brawler like Kiryu would be
sick, and Yakuza is packed to the brim with excellent characters, stage locations, and music to make for an extremely solid pack. Plus, a Heat mechanic sounds amazing, and would work as a reverse of Joker (get rewarded for hitting rather than being hit) and I think it would make for a super interesting character.
His stage needs to have a mechanic where
he shows up as a boss, though: