According to Google's Sundar Pichai, Google has no plans of stopping production of Nexus hardware. Google intends to continue "pushing hardware" in addition to the stock Android experience that is delivered by Nexus devices. Google will also continue partnering with companies to offer a stock Android experience.
"The idea with Nexus is to push on hardware as well, so that will continue," Pichai said. The last Nexus hardware that was released by Google was the Nexus 4, Nexus 7, and Nexus 10, all of which were announced and released last year. This year, Google has announced two partner device versions--the Galaxy S4 and HTC One--that both use stock Android.
Pichai didn't say when we could expect the new Nexus hardware, but we doubt it will be much longer. Maybe a white Nexus 4 with upgraded hardware?