NULL pointers working the way they do was a design decision made my hardware engineers a long time ago because it saved some transistors when that mattered. We’re past that point now for most ASICs and hardware can be changed. Although backward software compatibility is a thing too.
Null pointers have nothing to do with the instruction set architecture, except as far as they are often represented by the value 0. Can you describe the scheme you're imagining, whereby their use saves transistors?
Getting the chip stable is one thing. Getting all the various software applications that one uses test their chip is another, and a lot of hardware companies won’t have experience there. Then there is customer code…
