The effect is more pyschological than useful. This is weird but... it would be more for my personal enjoyment than anything else.
Go down kicking, style of thing. Yeah, I can see that.

Low HP, no more ammo, you're gonna die but you manage to get one last kick in. I guess that would be satisfying.
Not to mention that, other than the painsaw, humans are thoroughly devoid of melee attacks, so this little addition could be interesting.
From a practical point of view:
* Implementing it without actual animations is quite easy, from what I understand (don't flame me, I'm not a programmer).
* IMHO, the bsuits shouldn't be able to use this. Both for balance of the game (they already got a bsuit, they should find better ways to attack) and for realism (you got a suit of heavy armor on, you're not gonna be using your feet for kicking).
* For animations, I understand at least two things would be required: a HUD model of a leg doing the kicking motion; and an animation of the base model doing the kicking (for 3rd person viewing ie other players's POV).