I like your ideas, particularly the attachment machine and more map interaction. However I don't quite understand what the whole "Instant kill Element" section was about. Care to elaborate? Is it a nerf, buff, or new power up all together?
I think PHD flopper is fine as is, considering suicide bombing zombies by cooking a grenade and running into a horde is one of the GREATEST THINGS EVER.
I like the pro idea, it would save space but not be too OP as long as they balance the price.
A boss round would be great. A round where all the zombies are gone and you have to kill George Romero to continue, or something, and he gets harder every few rounds (Taking a cue from Gears 3 of course)
Semtex would be cool. I would even take it a step further and suggest C4. Imagine the suicide bombing plots you could create with some C4 and PHD flopper!
EDIT: Okay, I reread the instant kill section. I agree that traps shouldn't get insta-kill (Though most of them kill super good without it anyway), but grenades should remain as-is.