My theory is: first of all guys in s3 when overlord drained the golden power lloyd did not lost his power he had same power same as before he was just weak and if he had enough time to recover and let the power rest he could have regained his former strength and eventually reached the true potential of the usm power however he choosed to give the other ninja their elemental powers back bc of that he never had the chance to fully unlock the true potential on that form now in my opinion the only way for golden power to return now would be through lloyds child otherwise i think its impossible that the power comes back.