The Func button is not a feasible replacement (for me) for that AF-On button. For many reasons.
>> If enough buyers would agree to $2700 for a pro body DX...
Nikon managed to make the D300 for $1600 or so, with a "heavy body" if you want to call it that. I don't; I consider the D3 line "heavy body". I don't see any reason why that could not continue.
The problem I have with the D600 is not the D600 per se, but Nikon has apparently abdicated their commanding position of a market that made the D300 a huge seller for many years. I don't see that changing (unless there are more like me than many acknowledge) and that is sad. The end result is a 3x price increase to update (not upgrade) from the D300, and the D800 does not really replace the far more agile D700 (at 8fpx). It's a 180 degree reversal in marketing strategy that started with the D200.
I don't think those that do not shoot wildlife or sports understand the problem.