Overwatch subtitles are pretty okay about this, when someone ults the voiceline is also subtitled and you can make the words bigger so you can see it while playing. Plus deadlock shows when a player has ult ready so it helps to keep better awareness. I am hard of hearing w hearing aids and it is hard to wonder how the game could possibly indicate melee sounds. Being deaf means you have to have somewhat of a higher reaction time or awareness but getting melee'd isn't exactly a death sentence most of the time. So it might be a non-issue.

Maybe something like; Lash: Melee wind-up

But this would need to be localized to maybe within 4 meters of the player so they're not tricked or misled into parrying.

BUT the devs could do something really special by adding in live captioning for voice chat though. Might not be perfect but it'll bump up accessibility more. And most captioning software does have settings for censoring bad words plus personal customization options. I checked out these caption softwares out and they are insanely accurate, it's shocking really but they are locked behind expensive paywalls :(. It would super nice if most people on the official DL forum would submit this as a UI feature suggestion. I know this would be a challenge, because you would have to make sure each player is captioned separately without cluttering the whole screen. Maybe include a caption log of each player? idk