One curious feature unique to the N6 is its support for the new
Google Fi. In a nutshell, it's one phone number that will ring through to you over T-Mobile, Sprint, and/or your local WiFi, with a lot of back-end smarts about doing transparent handoff and relatively cheap billing.
It's still cheaper, for me, to stick with my T-Mobile family plan (4 for $100, with 2.5GB/mo/phone), happily supporting four users, but otherwise the Google plan is very attractive.
Personally, I'm sticking with my Nexus 5. If it blew up tomorrow, I'm not sure what I'd get. I'm hoping there's something new this summer, hopefully in the 5" class, Nexus-branded, cheaper, and with a USB-C plug. That will get me to switch.