"Oh no, I’ve fallen and can’t get up!"
Sucks to be you, Susan! Just walk it off, eh! 
No logic here:
Fair warning that this post (semi-ish) throws logic out the window. I have a poor memory and feeble mind, but from my understanding it hasn’t been that high in his wishlist due to limb-specific breakage (and such) being “rather un-fun” after it occurs.
- See, if I still recall correctly, Nelson doesn’t want people to end up with broken limbs because they won a firefight but the dude they killed was just spraying randomly and happened to break all your bones. (Similarly, this is why organs hasn’t exactly been all that high on the wishlist either). I could just be misremembering things though. It’s not relevant regardless(-ish)!
Is it unfun to suddenly have broken limbs? Maybe. I have the experience to answer, but I’m no professional in that field. What I can say is that we could manage to postpone that unfun-ness if it so happened to occur.
Ignoring the fact that some people may perhaps enjoy the stress of such a predicament, I’m going to make it less unfun (but only temporarily).
Adrenaline rush:
See, if your player character’s limbs suddenly plan to go… limb… (or whatever they do), the player could potentially get a short adrenaline boost that counteracts the penalties that have been brought upon the player. So, instead of suddenly limping around with two broken legs, you can casually strut your character around for a wee bit… and then go limb!
- (Obviously, not every damage source should even remotely have a chance at causing this, and the effectiveness of the adrenaline could potentially vary so that some penalties do still show through, just not that well [until the penalties fully overcome the adrenaline as the adrenaline rush fades away]).
That would, probably, help to make the mechanic less immediately punishing to players that just so happen to suddenly be unable to strut around as efficiently as they would’ve desired. It gives players time to react to their additional predicament without fully rendering them helpless. In a firefight, this means that limb breakage is still viable, but not a “basically guaranteed kill” immediately following it. Against Turned, this means that even if something rather large decided to smash you into a wall, you could still manage to (potentially) get away (although at that point you’d probably still be rather helpless).
A bloody trail:
You may be able to debate the whole “limb breakage is still viable” line, as we could theoretically say that nobody would intentionally even go for limbs if there isn’t an immediate reward (and thus it just furthers the original conundrum, and makes the feature rather “meh” overall). That could happen, but we could also just give some help to the attacker instead. Upon limb breakage from most damage sources, the player could also just end up bleeding a trail out (even during their adrenaline rush). This means that the hunting player would still be able to at least track down the soon-to-be-penalty’d player.
I don’t particularly have a strong stance on things like specific limb breakage to begin with, but I got the idea for this post and just wanted to throw something out there that may potentially affect other’s opinions (either regarding such a mechanic, or regarding how it should be implemented).
So, feel free to tear the post’s points apart if you want. Do that normal discussion thing.