If you are still on a grandfathered unlimited data plan then you already know that your plan does not include free wifi tethering. In order to gain that you would normally need to ditch your unlimited data plan and pick up a capped data plan. The good news is that with root you can mod your device and solve this issue! Enabling Wifi Tether on the Nexus 6 is as easy as editing the build.prop.
To Enable Wifi Tether on any Nexus 6
1. Grab the Root Browser App from the Play Store
2. Navigate to the /system folder
3. Long press the Build.prop
4. Select Open With
5. Choose the Text Editor
6. add the following line to the very end of the build.prop text
"net.tethering.noprovisioning=true"
7. Now save the file and reboot your device
That is all you should now be able to wifi tether on your Nexus 6 for FREE!!!!!!!
***Please note: Tethering without paying for it is a "theft of service" from your wireless service provider. You may be subject to additional fees &/or legal action if they can prove you've done so.