The Only hope for Most of the outdated Smartphones getting Android 7.0 Nougat is Cyanogenmod, and CyanogenMod Team has started working on Cyanogenmod 14 which will be based on Android 7.0 Nougat.
Cyanogen Team has just started working on CyanogenMod 14 (Nougat). There's still no idea how long it will take CyanogenMod to ship first Stable ROM. For Now Cyanogen is working to bring Cyanogenmod 14 to Nexus 5x. Other Devices will start getting CyanogenMod 14 Custom Roms (Thanks to Developers) As soon As the Source is out.
So, all of that is to say sit tight, and be happy that Nougat is on the way to a Cyanogen installation near you!
Source- CyanogenMod (Github)