It also says this in the article you linked:

Those who already own such guns will have to register them, including serial numbers, with the Illinois State Police.

So it would apply to new purchases, but not those already owned. I'm disappointed in AP's reporting on this, different parts of the article seem to contradict one another on what the law actuality does.

If he expanded the court now Republicans would just block his judicial appointments until he's out of office.

Not a car guy, but I imagine it's kind of similar to what happens to old rubber bands. They start to dry out and lose their elasticity.