Puerto Rico isn't going to become independent anytime soon- it's against Puerto Ricans' interest to vote for independence. Being a commonwealth has its problems- disenfranchisement, mostly- but an independent Puerto Rico would have the same problems as an independent Mississippi or West Virginia- it has little high-level economic activity of its own, and its (for Latin America; by national standards it's a basket case) high standard of living is kept afloat by checks from the mainland's taxpayers. If it declares independence, that goes, its economy will implode. PR has a fairly well-educated populace, so it would end up one of the better off Latin American states, but the economic loss wouldn't be worth it.
Now, once it does become a state, if it does, that could change. It's much poorer than even a state like Mississippi or Alabama, and the state legislature may well decide that the best choice for PR is to put heavy investment into education and try to make San Juan a high-tech city. But I don't think that's possible...Puerto Ricans speak Spanish, not English, which puts them at a disadvantage nationally; and Puerto Rico is far away from the American mainland. It may become a manufacturing hub (I was wrong, and Wiki corrected me): there's a large manufacturing presence. The problem is that Puerto Rico isn't really American, and never was- it's Latin American. The accidents of political ownership aside, its language, economy, culture, etc. all merit being grouped with Spanish America, not with the Anglophone north. There isn't anything wrong with that, but Puerto Rico will be the odd state out (even in comparison to somewhere like New Mexico) for a long time. It could become a second Florida, a warm place for Northeastern retirees to spend their golden years.
But for all that, I could be wrong; major areas of the Southwest are virtually bilingual. We shall see.
I do kind of wonder whether the introduction of PR to the Union might help trigger a wider political realignment. Puerto Ricans, as I said, are Latin Americans...and Latin American politics are not American politics.