I ... hmm. My memory is really, really dusty on that.
I remember I had a handful of conversations with Bryan Dube during development about Q4 deathmatch. He was a super sharp game programmer / technical designer who had done a ton of the work on Soldier of Fortune 2 deathmatch previously, and had worked on the Urban Terror mod for Quake 3 before that. And he was much more focused on multiplayer than I was.
We talked a lot about weapons (as I had done most of the code side work on weapons in Soldier of Fortune), but I'm now remembering him being really keen at the time on adding more high skill play to Q4 deathmatch. We all loved rocket jumping, and I remember him really wanting to add other kinds of high skill movement.
So that much I definitely remember. More than that and my memory is kind of fuzzy. To be honest, lots of team members loved deathmatch and Quake, and all of us were of course talking about gameplay possibilities all the time, so it's possible the idea originated somewhere else on the team.
Ah, yeah. If you go through the code there, Bryan had to change that file in quite a few places to implement crouch sliding.
Nick Maggoire is an animator. Super nice guy. No inside voice at all. I shared an office with him for a while :) I haven't kept up with him, but after Q4 he left for Valve where he's been ever since, it seems.
That comment strongly suggests to me that Nick did the animations for players crouch sliding. Or, that's my hunch anyway.
