There's enough partitions as there are, with all those UEFI and stuff a disk could look like Balkan states, divided in bits and pieces. I always trim to minimum number required and without UEFI, in my case, it's always ONE. There's enough programs to be able to make independent backup of it and be able to go back to it within minutes.
Without internet, very few things run nowadays anyway so distributing windows that way makes most sense. For others that can't or don't want to be online all the time selling DVDs or USB memory sticks is only way in any case.
Zillions of things run without internet
For example CAD/drawing packages, Photoshop, Office software of all types, Music studio software, Machine control and measuring software, and goodness knows how many other things.
It's perfectly valid and legit to want to use a computer ISOLATED from the Internet - and this computer could still be doing useful and productive work.
For a lot of people life without the Internet is inconcieveable --but it exists --lots of dedicated stand alone machines don't need e-mail, Twitter, farcebook, google, web browsers etc.
Remember also that a computer can also be connected to a LAN where the LAN itself isn't on the Net so stuff can still be shared if required.
The idea of a hidden partition is also horrible --in any case a lot of people often swap a usually "cruddy" laptop hard disk for an SSD anyway. A standard ISO image WITH NO BLOATWARE should be on the new PC - On setup the user should be prompted to make a bootable USB from the ISO. No Net required, No Hidden partition screwing up with your HDD's, and only uses around 3GB of the initial space. The user could then simply back up the ISO to external media as well and delete the image.
The start up software should prompt the user to insert a USB stick and then do the job so it would be SIMPLE even for a complete novice.
I unplug my computer at night and during storms. I don't know how windows 10 would even update at night. I also boot into windows 7 & Xubuntu.
Those are all for dedicated machines which can be very sensitive to any changes. Don't forget, we used computers for loooong time without internet at all but even than computers I used for coordinating and running production machines were tightly locked with only one port open so I could fix something for night shift over the phone line from home.
The makers also went to the "restore" partition because MS requires them to include a means of re-installing the OS. I guess the hidden partition was the cheapest way, as well as the worst possible way (as it's gone if the HD fails).
I like your idea, but it might be nicer if the makers provided write-protected USB flash drives as well. (Which most people would lose in a day or two, but what the heck.)
When I bought a cheap laptop (Compaq) in 2008, Best Buy offered a $50 service to get rid of most of the crudware. I didn't sign up for it, as I felt competent to do it myself. Turns out that they did it for every laptop as it came in, so I got the service for free. (Mildly amusing. I had all the time in the world at that time: I was unemployed, and I was mostly housebound due to a broken ankle. Which was why I wanted the laptop; too hard to keep the leg elevated at my desk.)