Shadow do you have any evidence that the amateur landscape shooters are where Sony took market share from Canon or that they took market share from canon at all? Do you really think that with IBiS and great high ISO performance and with increasingly good AF and such things as eye focus that Sony set out to and accomplished the task of taking market share from canon in the landscape segment? Also where does your theory of needing fast glass fit in with landscape photography?
I don't think anyone has actual figures. But the tone on various forums - DPReview, POTN, here and elsewhere - changed significantly between 2012-2014, as did the makeup of full-frame cameras I've seen in the hands of shooters on landscape photography tours and at prominent landscape shooting locations all over the world (I'm using full-frame as a marker to indicate more serious photographers, since many not-so-serious photographers and tourists have a low-end Canon or Nikon crop or an Olympus M43 body).
Prior to 2012, almost everyone used the 5D2 - it was everywhere, and probably still remains the most commercially successful full-frame digital camera released. But a number of comparisons soon emerged between the 5D2 and the early Exmor sensors used in the A900 and D3x, showing much better shadow detail recovery in the Exmor sensors and a disturbing tartan pattern noise in the 5D2's shadows. This did not translate into success for the A900 or D3x - the A900 had a far poorer lens lineup (among other issues), while the D3x was double the weight and triple the price and was generally far more limited when not shooting landscapes or studio shots at base ISO. There was low-level grumbling, but this was generally far outweighed about the grumbling about the AF and other handling features vs the D700 - most talk was about a potential '3D', with the 5D2 sensor and compact body but 1D-type AF (this was later realised in the 5D3). When Nikon released the D800/D800e in 2012 and Canon was unable to maintain the lead in either resolution or overall image quality, the grumbling intensified, but most people still stayed with the 5D2 (without upgrading to the 5D3), since they'd be unable to use their Canon lenses on the D800. This changed with the A7r, helped by Sony's inclusion of a free Metabones adapter with every A7-series body sold. At that time, there were a huge number of 5D2 and 5D3 bodies on sale in the buy & sell boards of every forum (including here). And A7rs started showing up everywhere landscape photographers congregated (Gorak Shep, Namche Bazaar, Patagonia's W-circuit, Erta Ale, among various places I first noticed the trend) - almost universally attached to red-ringed Canon L-series lenses. And the tone on forums changed, too - on landscape sub-forums, Canon appeared to be generally out of favour, with Nikon and Sony being the two main choices, and remains so to this day.
Sony may not have
intended to specifically pry landscape shooters away from Canon (although the inclusion of a Metabones adapter with the first two generations of A7-series cameras clearly intended an intention to pry photographers away from other systems - and, with the AF performance of adapted lenses, and AF performance of early-generation A7-series bodies in general, it was never going to be the action photographers they would pry away). But, intended or not, that's what they ended up doing. And it helped them a lot - without the influx of Canon shooters, uptake of E-mount would probably have been much slower, restricted largely to beginners and those looking for a 'compact solution' at first, and the evolution of the mount since then (assuming it wasn't stillborn entirely) would probably have taken a completely different track, focusing on compact, portable lenses rather than the fast, pro-grade f/2.8 zooms and f/1.4 primes we're now getting. It's probably not coincidental that two of the biggest camera stores around here sold almost twice as many A7r bodies as A7 bodies, despite the A7r being more expensive and more specialised. These days, whenever I go to shooting spots popular with landscape photographers (New Zealand most recently, Pakistan and Japan coming up), I see an almost-even mix of Canon, Nikon and Sony among full-frame shooters. Many of the Sonys are now attached to native E-mount lenses, but there are still a large number attached to Canon lenses. Very few of them are attached to Nikon lenses, though, likely due to suitable adapters for Nikon lenses being late to arrive, but also because Nikon shooters have had no particular reason to switch, since Nikon bodies already provided everything they needed.
Anyway this is about Nikon. I have no idea what their plan is and nor do you. I think but dont know that they are planning a migration path for existing Nikon users. This offering does that imho. Sony needed to break into the market. Nikon need to retain existing Nikon clients. That is working I believe and my evidence for that is Bernard and several friends with Nikon’s who are keen to give mirrorless a try. Two of them have 850s and the mirrorless gives them a more compact option that can be used with existing lenses should they wish to do so.
Obviously Nikon needs to try to retain market share. But intention is not the same as results, and perception is not the same as reality. And it's far too early to say that 'it's working'. There have been negative reviews (of preproduction models) already, mostly centering around AF (apparently similar to A7r2-level), and opinions among Nikon users I know have been mixed to underwhelmed, with most saying 'I'll stick with my SLR' rather than switching to mirrorless. In a way, Nikon is a victim of its own success - the new camera needed to outdo the D850 (probably the best all-round SLR out there, and by no small margin) but mostly fails to do this. If they had never released the D850, or if it had been a lemon, there would probably be more people interested in switching (assuming they didn't switch to Sony first).
The question is not whether Nikon is trying to provide a migration path - they clearly are, so it's not even a question. The more relevant questions are whether a large proportion of current Nikon shooters will follow this migration path, and whether it is even the best migration path to mirrorless for current F-mount users. After all, porting your existing lenses to mirrorless and using an adapter is only one of several possible paths to mirrorless. There is also the option of selling your entire lens lineup now, for a good amount of money, and buying an all-new, all-mirrorless system (in which case Sony would have the clear advantage), or sticking it out with SLR until your lenses become obsolete and are due for replacement anyway (in which case the advantage would be with whichever mirrorless system is dominant in 5-10 years' time). Nikon will clearly try to sell it as a migration path, and the marketing will reflect this. But whether it is the
best path remains to be seen, and likely depends on how many F-mount lenses (and which ones) you already have.