I would say the same thing if someone contemplated spending $800 on a Pixel to put an AT&T SIM in it. My concerns aren't with the network so much as it is with the Pixel's incomplete compatibility with networks other than Verizon (and maybe T-Mobile, which seems to be supporting the Pixel). As I said before, there's no Wi-Fi calling, Sprint isn't going to actively service the Pixel to improve call quality, and though many Sprint reps have probably been briefed on the phone, they still won't know much about it.
The Pixel is a boss phone, and Sprint is an OK network if you're willing to deal with some service issues (though I do have to say: their Unlimited Freedom plan is absolute garbage; won't be fooled into switching once my grandfathered unlimited plan ends this year). But at the end of the day, if I am on Wi-Fi without good service (aka in my house) and can't send a text, I could care less about how zippy the Pixel is. This is 2016; Wi-Fi calling and texting shouldn't be a luxury and flagship smartphones should have the complete functionality of the networks they're on.
Even without Wi-Fi calling, I have experienced poor call quality and signal strength on both my N6 and N6P - unlocked phones bought directly from Google. At the end of the day, a smartphone is still a phone. And my experience with unlocked phones on Sprint has been "it'll work, but not well, and dont bother complaining."