i dont know how easy it would be to put your proposed changes into a plugin but
in my humble opinion the easiest way (logistically) to nerf sniper would probably be to ban stock rifles and bazaar bargain (stupid but simple)
next most viable rifle would likely be hitmans heatmaker which has weaker bodyshots (40 uncharged, 120 fully charged) so we can keep awesome headshotting long range class (i dont know how the other attributes of the heatmaker would affect sniper play)
however, it doesnt really address the problem of sniper slowing down play outside of last, only remedies the most pressing issue by making getting value more difficult
sidenote: i think a lot of snipers at higher levels tend to not miss the head much, but in a vacuum this change would help
i also agree that unbanning unlocks would make it easier to battle sniper comps as well but talking about unlocks should be a whole other ordeal