Control the exchanges, you control peoples ability to enter and exit bitcoin. How are the Puerto Ricans going to get hold of their bitcoins while still avoiding the transaction tax?
P2P of course. How will bitcoin come to replace Paypal for Puerto Ricans, then, you ask? Well I would say, that's a damn good question.
I imagine there is nothing stopping Puerto Ricans from buying bitcoins on Circle or Coinbase, withdrawing them, and then transacting without this extra external fee. But this won't happen overnight, on the whole, by any means. The extent to which it will happen at all is a big question mark.