It is fairly inevitable that it will be a Nikon Z-mount version of the equivalent Sony lens launched AND launched September or October this year.
The road map shows it is NOT an S-line.
So it will not be a replacement to the 200-400/4G or 180-400/4E. AND unless they add $1,000 ir will not have an internal TC.
As a Nikon design it probably will be will be developed from the 200-500 f/5.6 and 100-400 f/4.5-5.6 - so a relatively budget lens ($1-1,500) -
such a budget lens is what many are calling for - who want reach but do not want to spend the price of something much longer. AND it does leave the door wide open for a faster 180-400 S-line with TC later - at 10k++
The Launch Event may well include the 85/1.2, 2 DX lenses and the 26mm (which looks like a compact, but maybe something else).
What is less clear is whether and when the Z 600mm F/4.0 TC VR S-line will be launched AND what new or updated Camera Bodies will also be launched-- I hope it is at the same time.
Such an event would be an ideal time for Nikon to issue an update to the Road Map to layout the next group of lenses (at least in outline) they anticipate producing to take them towards their target of 50.
Beyond the current road map most folk do not want another 24-> zoom or another long focal length glass. They want Wide and Bright Primes for FX and possibly DX to. From Ultra wide 8-15 Fish Eyes and ultra sha rpe bright primes at the usual FL from 14mm up through 135, 150, 185 and 200. Hopefully with a few longer focal length Macros in there too. I hope Nikon has the cojones to go for a bright 180/185mm MACRO f/2.8 or brighter
I do not currently foresee a 135mm f/1.? DC (Defocus Control) - but this would be a fascinating lens - the F/2 D version originally launched in 1990 and updated to a D in 1995 was special. A recent patent was referred to in another place.