This one isn't a debate about bone structure or "comfort" of sitting, but rather relates to animation.
We have a /sit command that causes the player model to run its sitting/sitting-loop animations. From what I've seen all the animation files are separate component parts so in [theory] it wouldn't be difficult to add a new animation (edit the CAL3D file to accept it, create new anim, and so forth)... I do acknowledge (from personal experience) that creating an animation is not as simple as saying "let it be so" but I imagine this is doable.
Anyhow, in the same vein that we have /attack1...5, perhaps a new /sit1 animation and game command for those of us who'd actually use chairs? Or even just an alternate sit command - doesn't necessarily have to be targeted towards chairs.
I know it's not a very high priority, but I thought I'd throw it out there.