Nexus 6 was released around early November 2014.
So I assume the next Nexus devices will be unveiled in 8 weeks and released around end of October/early November
Also, the people who buy Nexus its a different market from Moto (sort of, for example who wants a Moto G for daily driver won't be interested in Google's own High End phones)
It all depends on how Moto X performs and how many persons want to upgrade to either a Moto or Nexus device. But Android fans that only use AOSP will only buy Nexus for sure.
Their only other option is Moto or other phone with a AOSP Rom.
But in terms of sales it all depends, Moto X is really looking good in terms of price/quality.