I have used the now expired FAA piggy back licence extensively in the past to rent and fly aircraft in the US and want to continue to do that.
options
On your next visit to usa take a flight test with a examiner for a full ppl you would need 3 hours min with a instructor first and pass the written tests (computor )and a medical maybe some night flying if you don’t have some in your logbook but this can be done as part of your 3 hours min By selecting a AME or CFI that has both easa and FAA privileges they could validate both your licences in the future
at the moment you can get a 61.75 by applying to a examiner based in Europe /uk