for me, buying the Nikon F6 is in much the same (albeit even more expensive) category as buying a Canon EOS 1v - i.e. it's a chance to have the "last in the line" - possibly the "best" 35mm camera that one of the top manufacturers knew how to make, just as they were turning over to digital.
Of course, it really only makes sense if you're invested in the Full-Frame Auto Focus Lens Eco-system - taking the Canon point of view, if you've a full frame Digital Canon body, and a bagful of L lenses, and you occasionally enjoy shooting on film - or - strange as it may seem, get asked to do so by some wierd clients (yep, I do actually get that occasionally - usually hipster tosspot Bands, but WTF, they're paying a premium for it...) then having a film body that works pretty much interchangeably with the digital body is brilliant - and at s/h Canon EOS 1v prices it's almost a no-brainer (only reason I haven'd got one is that I've already got a EOS-3 which is probably 95% the same functional camera, just without the Magnesium Alloy Body...) The AF performance of the EOS-3 and 1v is pretty amazing - basically, the same AF sensors went into the top of the range EOS 1D's and was pretty much the same 45 point area AF with minor tweaks right through to the 1Diii in 2007 and beyond - albeit with faster processors improving the overall AF speed...
The F6 and EOS-1v bodies don't make sense with manual focus lenses, but that's missing the point of these bodies. They're the last gasp of 35mm Pro Film Bodies, meant to be paired with pro-level AF lenses. It really doesn't matter if they won't give of their best when paired with a £2 Russian 50mm screwmount lens from a car-boot sale - because they're not about that. Similary, it doesn't matter that the EOS-1v won't work well with canon's own FD lenses - it wasn't designed to, if you wan't "state of the art automation" from the body with the FD lenses, buy a Tank (T90) - or, if you want a more tactile experience, get a A1 or F1... or any number of the older types...
So - I know I've banged on about Canon here - but I know the Canon side of things, and while I've never spent much time shooting with Nikon, I appreciate that they're the other side of the coin to Canon - and the rivalry between the two companies was what drove the advances in technology along - so, I'm pretty happy to say that the F6, being the last ever pro-quality body to be in production, is definitely going to be the most advanced way of shooting 35mm film stills - and all of the observations of it only really making sense when paired with full-frame, pro-quality lenses from Nikon's top shelf kit are going to be equally true as they are with the EOS-1v.
For many, the fact that it feels pretty interchangeable shooting with the "last in line" film bodies or a modern Digital body takes something away from the "film experience" - and I can appreciate that - there ARE times when I want to have a "bare metal" interface - just me, a manual camera, manual lens, hell - manual shutter wind and release if it comes to it... Dammit, I even shoot with pinhole Holga's occasionally - can't get much less automated or unsophisticated than that. But equally, there are times when I want the result on film, and I have to get the result, and, for those times, I'll admit it - my faith in my own perfection wavers, and I reach for the EOS-3 and the L glass... I know, for example, when I bought my last roll of Kodachrome - there was only one camera that roll was going in - I wanted all 36 frames properly exposed - ok, the subject matter may have been crap, that's down to me - but the technical exposure of the shots was bang on the money 36/36. And I knew it would be, because, in the past, I'd spent a short time working as ships photographer on a couple of cruise liners, shooting upwards of 15 rolls of 36x per night, in "mixed lighting" dining rooms, and over the space of 2 months I basically lost 3 frames from technical failures (each time I missed the battery warning light !)