Do you think Nikon could challenge the X system with something like this (pix)?

My guess is that the first mirror-less challenge to Fuji is actually likely to be Sony - the much rumored FF NEX9 or whatever they may decide to call it. They've released the RX1 fixed lens camera. They've said publicly that they're considering an FF NEX, but that the constraint is not the technology, but the need for a suite of matched high grade lenses - they haven't got them. Yet.