Alright, after trying out melee with the "use fire as melee button" option turned on and off, and I have to say that having the option turned on feels like pre-2.9999999 melee mode with the exception of the fact that I can't manual block or glide. Blocking was near useless anyway, but not being able to glide really stings, so I suggest that when/if you kill channeling, use the button to turn on aim-glide and toggle between stance combos and quick melee combos, that way you give the player the ability to aim-glide without forcing them out of melee mode and you give them back their quick-melee if they want it, all the while preserving their new ability to just aim and shoot on the fly. An added bonus is that you could also use it to toggle between our current directional aerial attacks and the yet-to-be-implemented aerial combos. For players that are complaining about combos being clunky and not meshing with the parkour movement, this would give them the option to pick and choose between a simpliflied-but-agile "quick mode" and a complex but rooted "stance mode".
So to clarify once more, the way this button would work is that the player starts in a "quick mode" that defaults to quick-melee behavior. If they press/toggle on the button, they now use stance combos instead, and glide if they are currently airborne. If they then release/toggle off the button, they revert to quick-melee, and resume falling if they were gliding in the air. I would expect some sort of visual indicator of which mode they are in, perhaps keep the channeling animations to signify that the player is in stance mode.
TLDR: I want to be able to glide while staying in melee mode again, but I like aiming and shooting when I see a nullifier or osprey, so I think another button that allows gliding for melee would be good.