Under the 2010 Census, with no other state losing representatives, Puerto Rico gets 5 Representatives. It would have gotten 6 with the 2000 Census numbers. It likely gets 5 in 2020, with or without a return to 435. And I think a return to 435 is likely. The small states perceive they have more political power with a smaller House.
I don't know if a substantially larger House is possible, but I could see the House increasing in a way as to not make PR statehood penalize the states that would lose representation. An even-numbered House is taboo (and for good reason), so 440 would not work. I don't know if there's a certain number that sounds good, but maybe something like 441 (or even 445 or 449). I'd say it's unlikely the House reverts to 435 with PR statehood. (Note that even with the DC Voting Rights Act, the proposal was for a permanent increase to 437.)