Good decision! Straight forward and concise.
I will add that those previously convicted may not necessarily have their convictions overturned. Under federal constitutional law, a case announcing a
new rule of law cannot be used to overturn previous convictions unless their direct appeal is still pending.
Teague v. Lane, 489 U.S. 288 (1989) available at
http://supreme.justia.com/cases/federal/us/489/288/.
Teague and its principles are difficult for lawyers and judges to apply because there are a million shades of grey in whether a decision is announcing a new rule of law. I won't pretend to know whether this Illinois decision is "new law." Of course, Illinois can give greater retroactive effect under state law if it wants to do so.