As Seth put it, it is apparent that regions do in fact exist beyond Hyrule, and have been visited before in the series. Examples include the aforementioned Labrynna and Holodrum, and how can we forget Termina and the WotOK? That said, I wouldn't mind visiting another region, realm, or kingdom in a future Zelda title, but I don't think it is absolutely necessary. It would be nice if there were a few more [new] towns, villages and/or settlements scattered about Hyrule Field [in the next Zelda game], though.