As far as your question: "Do you think they will keep playing all-court tennis as they progress in their careers?" , I can only offer my opinion about Berankis as I don't think that I am qualified enough in tennis to make any statements about others that are mentioned.
I think Berankis will keep being an all-court player whether he is willing or not, because he doesn't really have a choice. He doesn't have one very strong weapon but is pretty solid in all aspects of the game (one could make an argument about serve, his serve has really been a problem recently), therefore he often HAS to outsmart his opponent by constructing the point in his favor if he wants to win. I don't see that changing, I think point construction will be an absolute key throughout his career.
I think maybe it's similar with Harrison, but as I said I am no expert