"Am i right in assuming the bulk of issues have come from later or newer generation batches. Its seems to happen shortly after arrival or after a little use ??"
Regarding new vs late model, I can tell you I'm in Canada and received mine in January, SN 4000702. I've had about 10 lockups, only one and then it would work as it should for weeks. I'd estimate I've had one lockup per approximately 50,000 shutter counts. Yes, over 500,000 now. Nearly all my usage is 20 fps, no video.
I've updated my firmware within a day of it being available. I had about 5 lockups berfore 2.11, about 5 after 2.11.
Like you, I hope and trust that Nikon will make good on it as they did with the D600 oil issue. However, the fact that the warranty has been reduced from 5 years to 1 isn't reassuring.
I hear where you coming from.
There are company's that are very capable in designing and dealing with software, there are others that buy under license hybrid or parts of generic type software and blast off with retailing their products.
We have a national bank here that is considered world standard with its App and software security only second to one bank in Germany, we have other banks here large national ones who have built their software and security over time in an add hock cheaper rushed way to save and make more money, they have been plagued with on going issues due to their hybrid software construction of systems. Today they have become vulnerable and now need to invest heavily in lifting their game, sometimes cheap isn't the answer.
Why would you as a multi Billion $ organization not be capable of delivering reliably what others can, internal politics another word for pressure from the top or its cost cutting.
This issue is not about if its large or small, its about a consumer who doesn't know if the brakes on their car are suddenly going to not work when needed, that is the real issue.
I am leaning towards it being more a design issue given the history of some symptoms going back to January, if it was faulty components it would usually be known isolated and over, given the issue is escalating seems to be coinciding with software updates............that could have fundamental issues, i certainly hope not, but we cant help wondering, am i worried, hell year, it shouldn't be an issue at this level of product and company.
In one hand we call this all advancement in technology, in other ways its possibly a step backwards, but to me its all a move away from enjoying photography as you almost need to be Geek or IT expert to live with it all........as we do with our dam computers...........that's not photography as i knew it.
My D3x D4s were flawless for years and years and took stunning photos i enjoyed making, i could hang my hat on them 100% period.
Now i have to take a back up system and prey things don't go wrong while away or doing an expensive shoot.
Am i concerned, like many others yes rightly so
Only an opinion