OK, I stand corrected on Poland's rule on thier dual citizens. Extremely odd, though. Of course there are no exit controls when leaving PL for another Schengen country, so enforcement of this rule would seem rather theoretical.

OTOH, if you're an EU-citizen, any future ETIAS would not be a concern to you. For a great number of US-EU dual citizens taking (back their ancestors') EU citizenship is driven by the ability to enter and stay in the EU under rules for EU citizens.