I’m entirely aware that Puerto Ricans are Americans.
I’m on the island about every 2 years. San Juan is a lovely place. Arecibo is a great little day trip.
That said they are not culturally or ethnically or historically American. They were a prize of the wars of the Monroe Doctrine.
The independence movement there still has about 1/3 of the population on their side. Another 1/3 is ambivalent. And of course the final 1/3 is pro-American if not statehood. But their main connection to us is monetary: as an independent island they would starve. As a vassal state of Spain, they would merely be underfed.
Perhaps a CommonWealth status with limited immigration rights. Remember the British already went through this in the last century, and their liberal immigration rights from the colonies has resulted in the streets of London becoming a threat to the English themselves.
“As a vassal state of Spain, they would merely be underfed.”
I can not think of a single reason why Spain would take PR back into their fold. PR would be nothing but problems and expensive at that.