The other day I convinced myself to flash CM 12 on my HTC One M7 without GApps. However, within a couple hours had no choice but to flash it. Open Whisper Systems doesn't provide Signal's APK outside of Google Play (surprisingly Spotify does), and neither does Pebble. In addition there is some bug in messaging that prevents me from sending any SMS at all. I'd argue that GApps is a requirement for any Android device today. Unfortunately I see the iPhone as the only smartphone where it's even possible to avoid Google services.