Just a quick update, here's the reply from Ikelite:
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Thanks for your support of Ikelite products.
According to my records, Nikon updated the ED lens to add VR in late 2012. Unfortunately the raised switch on the side of the VR version prevents zoom operation with this particular lens. So the lens you reference B&H site can be used without zoom.
A popular zoom lens for full frame cameras is the Nikon 16-35mm f/4 which can be used with the 8” dome and does allow zoom underwater.
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So that's the definitive answer. The Nikon 24-85mm is NOT compatible with the housing if you want to zoom underwater although it WILL fit at a fixed focal length. This is as a result of the slight re-design Nikon did.
As far as I'm concerned, that might be good enough: I want a medium zoom for portraits, that's where this all began. This particular lens is considerably cheaper than some of the others I have been looking at, and gets superb reviews above water. I would be able to use it underwater at various lengths, and 24mm isn't at all bad if I want a wide angle lens for my dives. Sure, it isn't 18mm but a compromise needs to be made somewhere. It also jives well with the "choose what you want BEFORE you go diving" theory; stick in a particular zoom distance and live with it.
What I may also do is consider bringing my Sigma 105mm f/2.8 macro lens on the next trip. Then I've got the whole lot covered: 24mm wide using the dome port from the new 24-85mm lens, 50mm prime with a flat port which I'm already familiar with from my Amilla Fushi trip, and the 105mm macro for real close ups.
I shall start a new thread to ask about dioptres and flat vs dome!
Thanks everyone for you input.