Like a shield or regenerative armour that is there, so long as the song is playing?
I wasn't thinking of anything visual like adding yellow or blue bars of health to a character, was thinking more like simply percentage less damage taken. Just spit balling. He would need a second song that is worthy of playing. Maybe offensive fits better since heal song is already a defensive aura of sorts. But like I said, if it's too strong and he's the only character that can provide it, he would once again be a must pick.
Essentially since Lucio has two songs and only one of those songs is repeatable by other support characters (healing), giving him a second song that nobody else can do makes him a strong pick and with speed, he's a MUST pick.
The ridiculous thing about further nerfs to his healing is that it makes it MORE likely that he will play speed song exclusively. If he is no longer an effective healer, he has no reason to run that song except as self preservation.