Mandating English again in Puerto Rico schools may actually accelerate the depopulation in the short-term as many of the youth, fluent in English, are easily able to find higher paying jobs in the States.
In the long-term, you may have more people Stateside start moving to Puerto Rico since the beaches and surfing are really nice, and won't have problems getting a job (even if they can't speak Spanish).
From 1902 - 1948, schools in Puerto Rico were mandated to teach in English, when it was repealed to leaving English as a second language.
Governor Fortuno tried to impose English again in 2012, but was opposed by the Teacher's Union (of course).
The result of the system is that you have Private Schools which teach in English, and the Public Schools in Spanish. The wealth gap only widens as the rich kids learn English, and then can get higher paying jobs off the island. The poorer students forced in the Public Schools end up getting trapped on the island (and ironically stuck with all the tax bills the rich kids left behind after graduating the heavily State-subsidized Universities).
The current situation of Puerto Rico would look much different today (better?) if the vast majority of the population could speak fluent English like the majority of States.
Obtaining a political solution at this point, due to the demographics & Democracy, would be essentially impossible. So, I'd expect that PROMESA or some outside creditor will need to impose it on Puerto Rico against the "will of the people." (Of course, in today's climate, one simply needs to scream "racism" and "colonialism" if a mandated English language program was ever attempted.)
The basic premise being that the ones who are motivated or care enough to learn English have already moved off the island. This leaves a disproportionate of people who chose not to learn English fluently to stay on the island.
When I offer this solution, I am going against my self-interest. Should the island become linguistically equal to Southern California, you'd most likely have a lot more "Gringos" transplant to Puerto Rico and Statehood would be much more likely. If Statehood happens, then I would be out of luck on my Tax Credits.
Now, here's another layer of complexity: Section 936 of the Internal Revenue Code that gave tax credits primarily to pharmaceuticals and electronic companies. (It was ended in 1996, with a 10-year grace period, which is primarily blamed for the economic collapse of Puerto Rico).
Section 936 had a precursor, called Section 931 since the 1920s. English was removed as the primary language in 1948. Puerto Rico became a commonwealth in 1952, "where the Constitution stated nothing about the official language that would be used by the new government." Was it merely an oversight or intentional?
Assuming that the 1952 Commonwealth declaration took years in the making, I would not be surprised if the big money benefiting from the tax benefits aided the removal of English as a primary language in 1948. Perhaps they had some say in the missing official language in constitution as well.
If the big money knew Commonwealth status was coming, they'd also have to anticipate that having a Puerto Rican population that speaks primarily English (with many Statesiders mixed in) would eventually result in Statehood. Statehood would eliminate their tax benefits.
I have no way of knowing for sure unless I do more primary source research leading up to the 1948 language change, which I also expect will be primarily in Spanish.
If what I'm saying is true, it would confirm my suspicions that Puerto Rico is purposefully left in a weakened state to ultimately benefit the elite who find ways to take advantage of the tax peculiarities and/or "loopholes."
On a side note, this was an interesting article I found out that discussed the anomaly in data for the English speakers. The timing is interesting in that it is in 1948 when English no longer became the primary language in Public Schools. https://www.jstor.org/stable/25612889?seq=1#metadata_info_tab_contents