Google's Daydream VR is no longer out of reach to those without a Pixel or one of the few other supported devices, but the list of devices that can indulge at this point is only as long as the list of devices which can run Android 7.0 Nougat or higher, and which can be rooted. This includes a number of 2014 flagships like the Samsung Galaxy S5 and LG G3, as well as most Nexus devices. The process is actually pretty simple once you're rooted, provided you grab Google VR Services and the Daydream app from somewhere first. Once you've done that, it's just a matter of modifying the system file that determines what hardware features of Android your phone has permission to use. This method was discovered by a Redditor who goes by the handle of CharaNalaar, who tested it on their Nexus 5X.
With your preferred root file explorer app, enable system read and write privileges, then go to the base directory of your device. From there, go into the system folder, then into etc, then permissions. There, you'll find a file called handheld_core_hardware.xml. Open this up with a text editor or hex editor. The notepad built into some more full-featured root explorer apps like ES File Explorer should do the trick. Find the root permissions tag, and add in this line: <feature name="android.software.vr.mode" /> <feature name="android.hardware.vr.high_performance" /> . After adding that line to your XML file, be sure to save it as you exit, then reboot your device. All of the Daydream apps should work fully, and you should be able to download more or update your existing ones from the Play Store.
This method unlocks Daydream support for devices that Google has not certified as being able to withstand Daydream's heavy demands, which can even make a Google Pixel or Pixel XL get hot under the collar; this means that running Daydream content on phones with heating issues or any sort of instability is probably a bad idea. You should also go into the whole affair knowing that you probably won't get performance that's totally up to snuff, even if your device has a Snapdragon 820 processor or better in it, due to a lack of optimizations for Daydream on your device. If you're having any real trouble, you can try disabling the VR intro screens. This setting is found in the Developer Settings for the Daydream app, which can be unlocked with a few taps on the build version in the app.