Yes, I think lots of Canon users would have loved to switch back when the D3x was released, (and many did). The D800 series was a total reversal as Canon was now the one who couldn't respond quickly enough and many Canon users did move back to Nikon or just started to shoot with both systems, (as I did), in order to reap the benefits of that amazing sensor.
Canon and Nikon are both great systems. The mainstays. The rest of them are either "also-rans" (or, in some cases, up-n-comers, but not "there" yet. Really, not even close).
The big difference, though, to me, is
Nikon has stayed connected to its past.
Thus the history, the roots, the sense of connectedness seems to be deeper amongst Nikon users than Canon users.
(And rightfully-so.)
I love some of Canon's newer lenses, I really do, and I think their 1DxII is probably the better buy between it and the D5 ... with FAR better 4K capabilities (although, I suspect, it will not be in the same league as the D5 in either single-image quality or in low-light performance).
However, I am lukewarm about Canon's low-to-mid-level cameras.
For most consumers, Canon's midrange is simply weak compared to (virtually) everyone else.
The way I see it, since the 5DS-r already isn't as good as the D810, overall, I can only imagine that the soon-to-be-released D900 will blow make the Canon 5D away as an embarrassment, in the same way that the D500 will immediately render the 7DII anemic and sickly by comparison.
That said, this thread topic wasn't intended to start a "brand debate," but to tip my hat to the fact Nikon remains connected to its elder lenses (many of which are quite remarkable, and useful) which, because many are so inexpensive to get a copy of, makes it kind of fun to plan and experiment with.
Jack