Price is still a factor here. The Canon 100-400 is nearly half the price of the Nikon 80-400. It seems to me that a Nikon shooter wanting to shoot a D400+80-400 is going to drop potentially $6000+ after taxes.
This is why I say Nikon is not really all that interested in this market. At least not for hobby wildlife and bird shooters. How many will spend that? This is not a volume market.
Of course a d400 could still be coming, this might explain why it hasn't been a huge priority though. Nikon took its sweet time upgrading the 80-400 for instance. It was rumored to be released constantly for years.