While non-Pixel smartphones and tablets will have Android Nougat (some Nexus devices already have the software), what they won't have is Google Assistant. This is a feature which will be limited to Google's newly announced Pixel and Pixel XL, at least for now. It is however, possible to get Google Assistant working on devices other than the Pixel phones as long as Android Nougat is installed on the device. As reported, it should be possible for any device that has Nougat installed to enable this functionality, but there is always a possibility that it may not work for some devices, so that's something to keep in mind.
With that said, the process for enabling the feature is actually pretty straightforward. Other than having Android Nougat installed on the device, users will also need to have an updated version of the Google app, with it being at least version 220.127.116.11. From this point forward, the steps needed to turn the Google Assistant feature on requires just a few things, although it is worth mentioning that it's perhaps not a good idea to try this if you aren't familiar with the terms and or how to get to these functions.
To get started, you'll need to have your device rooted, or you'll have to at least have a custom recovery installed on your phone or tablet running Android Nougat to initiate the following steps. If this is already in place, then you'll need to do one of two things with your build.prop, which is add two specific lines - "ro.product.model=Pixel XL" and "ro.opa.eligible_device=true" (without the quotes), or you can replace the corresponding lines that are in the build.prop with the ones listed above. If you aren't sure which lines these would replace, simply adding them might be easier. Once this is done, you will just need to wipe the data for your Google app and then Google Assistant should work. This process is the Root method. If the device is not rooted, or if you don't wish to employ the root method, it's also possible to flash a ZIP file which takes care of the process, and for this the custom recovery will need to be installed on the device.