Is a pacifist route even possible?

Not if you want to beat the game, but it would be possible as soon as you want to do something else. Maybe something like getting the maximal percent you can get without actively killing something (meaning that fighting hornet and the aspids dying in the aspid arena through falling spikes that you do not hit would be okay) could be interesting.

this is a link to a guy who did a no soul challenge run of hollow knight. He beat the entire game while using only one major glitch (airwalk) and never collected soul. www.youtube.com/watch?v=fVxK-2j3kwU

@discmaster it's not airwalk, it's p(ersistent) float