Commercial niche markets exist because the suppliers have large profit margins.
If a manufacturer can sell 10M phones per year and make $10 profit per sale, that's $100M.
If they can only sell 1M PCs per year, they have to make $100 profit per sale to equal $100M.
How much profit does an OEM make on a $300 desktop?
How much money does it cost component makers to design, market and stockpile a dozen slightly different motherboards?
MS is willing to forgo a potential income of several billion dollars per year by not selling updates for XP (100M PCs x $50/yr).
I willing to bet that they wouldn't have to spend much money ($10M?) on programmers to do the job.
MS could still sell millions of copies of W7 and every sale would be pure profit, but they don't.
The average user doesn't like "computers", unlike (possibly the majority of) TenForums members.
If they only use Facebook and write a few Word docs, a terminal is more than adequate.
Governments (specifically Acronym Agencies) will eventually start pushing manufacturers to remove capabilities from devices by claiming their latest stupid plans have been thwarted by (for example) encryption.
See the current US (and other) governments vs Apple debacle.
Apparently no crimes were ever solved before the release of Smart Phones.
As for prices they won't go up too much. First, because with standardization, the parts that go in a 2in1 go into an ultrabook or laptop. The parts that fit in a tower fit in a mid-range server. Graphics cards are the exception, but then enthusiast cards have always been expensive. Also, with a saturated market, if the prices increase in an effort to boost the bottom line people will simply hang on to their devices longer because they can, and in many cases already are.
Personally, I think there isn't a next big thing for the PC market. We have every shape and size there is. The market expansion will be found in niche products that make sense to interface with our devices. I can control many features on my car via my phone, and get monthly reports on its health. Other folks control their home security, hvac etc.
While Microsoft and its marketing of Windows 10 has been a pretty big fubar, their vision is not. The future is found in the services and the devices that use those services. I'm just thankful to have been in this industry long enough to see it go from roach chips, jumper switches, and soldering wires to where it is today.
In poorer countries (from what I can tell) people buy mobile devices (phones/tablets) not desktops/laptops.
One of the last exercises we had to do in my Web Desgin course, was come up with a website that would allow eye doctors access to a stockpile of surgical videos.
The doctor who created the stockpile, stated that the project needed to be biased towards smart phones, as the doctors in poor countries had smart phones, but almost no one had desktops/laptops.
Phones/Tablets are ideal candidates for reduction to terminal-style machines.
It's also responsible for MS (and some Linux Distros) flailing around trying to bolt mobile interfaces onto desktops.
I would assume that in the desktop PC market the sub-sector with the greatest churn is Gaming PCs.
Gamers always seem to need to buy new stuff and they don't seem to care about the cost (unlike Home PCs and/or Business PCs).