According to reports, it seems Google's focus is on making the next crop of Nexus devices durable and future-proof. It should be interesting:
Nexus 5 2015 and Android M born to be together - GeekSnack
Google Nexus 2015 Release Date Update: Next Vanilla Android Flagship Is Durable & Future-Proof : Tech : Yibada
Nexus 5 2015 and Android M born to be together - GeekSnack
Google Nexus 2015 Release Date Update: Next Vanilla Android Flagship Is Durable & Future-Proof : Tech : Yibada