Who are their lawyers?
"an indicator of eligibility"
This is typical of the tech companies thinking that even when they don't get to make the rules, they still get to decide how to interpret the them. However, as Apple lost the case, they are subject to the ruling, which applies to all EU citizens. And it is a right, and not something you have to earn or lose* as decided by a third party. Not doing this could be could be considered contempt, and I'm surprised their lawyers didn't quash this idea immediately to avoid additional difficulties. It would reasonable to ask how the European Commission how to determine this, though proof of id is possible in nealy all, if not all, EU member states, though it won't be that hard.
* It's virtually impossible within the EU to strip someone of their citzenship once granted, unless malice aforethough, fraud, etc. can be demonstrated.