I think it's only a matter of time that North America produces another great player and by that I don't mean Raonic. lol. But somewhere there's a baby Sampras still asleep unaware of his future in some mother's womb.
Never say never but I don't think GB will ever produce a player with a big serve. I mean look at Roddick. He didn't have a very solid ground game and yet he maximized his ability by relying on his single weapon - his serve. And now there's the likes of Isner, Raonic etc. with their big serves. And they will continue to produce big servers who will be quite lethal on multiple surfaces in the future. Even Agassi had a very consistent and occasionally big serve.
Andy's first serve is big and effective but it's not at all consistent. If it had been then he wouldn't have to go for the 2nd so often.