Google might actually name the phone Nexus 4 (2013), like it did with the Nexus 7 (2013) tablet this year, and could do with the leaked Nexus 10 tablet as wel - these are the arguments extracted from the prototype leak running early build of Android 4.4 KitKat...
Source: http://www.phonearena.com/news/Nexus-5-to-come-as-Nexus-4-2013-like-Google-did-with-Nexus-7-here-are-the-arguments_id47939
Source: http://www.phonearena.com/news/Nexus-5-to-come-as-Nexus-4-2013-like-Google-did-with-Nexus-7-here-are-the-arguments_id47939