Well, technically if they were Str 10 AP1, the only change that would make to Infantry is to characters. Str D still 'only' wounds on a 2+."remove everyone hit"
Why not just lose Instant Death, but ignore Invulnerable Saves?Strength D is made strength 10 AP1 armourbane, fleshbane instant death and forces rerolls on successful invulnerable saves?