This happens with every single expensive headphone release: a bunch of people claim that it is over-priced without any evidence that it is.
Something's eventual price is a combination of a number of factors. R&D costs, manufacturing costs, marketing and distribution costs are part of it, and then it comes down to how many they need to sell and at what price to make a respectable return. This is less of a science. You can make it cheaper and make less profit on each unit and sell more, or you can make more profit on each unit and sell less. There is a sweet spot and it comes down to how many units they realistically expect to sell.
Just barrelling onto a thread and accusing a manufacturer of trying to rip people off is pretty short-sighted. We don't know the figures attached to any of the above. We have no clue, so what are we really trying to say? That we'd like it to be cheaper because we can't afford it?
For me, a headphone of this price is too rich for me to consider buying it right now, but that doesn't bother me at all. I don't see my personal budget as the ceiling of what a headphone manufacturer should strive for. I don't get angry that things exist that I can't afford and I don't claim they should definitely be cheaper just because I want them to be.
Sennheiser alone make headphones for people with a £100 budget, a £200 budget, a £300, £500, £1,000, hell £30,000 budget. That's just one manufacturer, there are good products for everyone at every price point.
We don't know how much more these cost to develop and make than an HD800S. We literally have no clue. It's clear from just glancing at them that they cost more to make than the HD800S, that's for sure, but I don't pretend I can glance at a photo of a product and determine that a £600 increase in price is definitely over the top. I also don't claim its definitely fair. I don't know. Anyone who acts like do is talking nonsense.
What I will say is this: the engineering problems in developing high-end closed-back headphones are a lot more complicated than those facing open cans. That's why open cans exist: a capitulation over the fact that it is just too difficult to get good sound without letting the backwave from the drivers escape. Since open cans were invented (by Sennheiser in fact if I remember rightly) the attempts at making closed back cans that were genuinely uncompromised have largely been unsuccessful. I can count the closed back headphones I would really call contenders on a single hand and have fingers free.
Maybe the HD820 is yet another failure. Yet another high-end manufacturer thinking that sticking a back on an open design and hoping for the best will have to do (mentioning no names here, but there are headphones out there that cost a lot more than these that don't do much more than this, and suffer for it). But if they have cracked it, then it is a big achievement and likely took a lot of research to get there.
If this beats the Mr Speakers Ether Flow C, then it is worth £2,000 as far as I am concerned. So let's just wait and see.