I've had a Google Fi Pixel for a few months now, but one of my key use cases of any mobile phone is reachability. With DialPad my phone can ring either in the app or to the phone, depending how I have it set up, but I tend to prefer the app, as I'm usually in WiFi or LTE environments. With GoogleVoice, you can't set a Google Fi number up as a destination. But there is a way around it.
Go into the Hangouts app and turn it on to receive calls. Set up Hangouts to ring accept incoming calls on your Pixel. Now your calls to your GoogleVoice number will ring on the Pixel. What I can't do is send SMS's or originate calls from Google Voice on my Pixel so it's still not perfect but at least the calls to me can now be answered on the Pixel...I'll take that as a half victory.