To be honest, I only really care about the "stock" nature of the Nexus line insomuch as it means I get exceedingly timely system updates directly from Google. So long as whatever Nexus morphs into is still Google-controlled to the point where immediate (or nearly) OS updates come for it without a carrier or 3rd party manufacturer middleman making the process take months, then I will be content I think. It's not like Google's own UI design language will change because of this.