SIZE MATTERS
That principle isn't going to change ... every advancement in sensor design for 35mm will be met by sensor design for MFDs ... only the sensors will be twice as big.
You are clearly correct but with respec' I think there's a point being missed: for sure bigger sensors will,
ceteris paribus, be better - but
ceteris are NOT
paribus! To continue going stupidly latin, by
reductio ad absurdum you would end up with a sensor the size of a sheet of 10x8 or bigger. The reason you don't is that you'd need vast lenses, huge cameras, tripods like the Pyramid of Cheops and Arca would be churning out Cubes the size of RVs and charging accordingly.
MFD is
already a compromise between quality, cost and usability. And if you want to use a DSLR type body on it you have to use a FrankenBody with a shutter like a barn door in the wind, no really sharp wides and no real telephotos because they'd be too huge. Otherwise you go for a technical cam and end up fighting colour casts and using a focus method that hasn't changed much since the 1800s.
So I think what those who are most interested in these high pixel count 35mm size sensor DSLRs are saying is: "I want smaller, lighter, cheaper, cameras and lenses that offer Live View, quiet, slap-free shutters, high frame rates, clean high ISO but I also want resolution that allows a 40" print. Maybe Video too. I want all this without making
significant sacrifices to noise, DR, perceived acuity and colour depth."
The weasel word here is
significant. It is up to the individual photographer to judge what (s)he is losing and gaining in all these trade offs according to how they interpret that word. If in a variety of 40" prints I can't see a substantive difference between the D800e and the IQ180 of course I will sell my IQ180. Without question! Provided of course I am happy that I have an equivalent selection of glass and we all know that might be the problem.
I have read the LL report where various luminaries couldn't tell prints from MFD and a variety of smaller form factors and whilst I would like to flatter myself into thinking that I
would be able to, I'm not delusional: if they couldn't, I probably couldn't. It's not enough to have shivers of joy when looking at a file 100% on screen - that is nice but it is a solitary pleasure.
So at some point a number of MFDB users will certainly jump ship. That point will be when a DSLR 'gets there' for them and that day is clearly getting closer, whether or not the D800 is its harbinger.
I had an S2 for a while, the first one in the UK. Great camera. I got rid of it because it fell between the stools,
for me. I am not price sensitive, I just want the right balance of usability and quality and I feel that balance shifting in my favour.