When I received my new Dell Latitude E7470, I installed immediatly a Debian testing (Stretch) on it. This laptop, is really, really great, and is working like a charm with Linux. I still have to install manually a WiFi firmware iwlwifi-8000C. A simple « sudo dpkg -i *.deb », and it worked quite well!
Recently, in the beginning of 2017, a Debian update (maybe to due to testing freeze? Or something else?) has broken it… The WiFi was not available anymore, as if no WiFi board were loaded! Let’s fix this!