Its definitely a very good idea, but it would need tweaking for sure. Perhaps a health bonus for zombies or something in the last stand. I only say this because if the human is last man and he is caded, then he has an even higher chance of winning than usual. But I like the idea a lot.
Last Stand
Zombies get revived, but no respawning
They have +200 health
They break ONE nail every time they hit a cade, and then they break a prop and aegis board in one
Humans gets 4 times ammo regen
Gets the speed boost
One hit from anything but a fastie is a instant kill.
That should make it so that its more on the challenging side.