I'll grant you it seems a bit dystopian, but as someone who has been in the IT field for 20 years and has an engineering background and an MBA, I've seen this coming for a very long time... it's where things are going ; or, at the very least - where Microsoft is going to try to persuade everyone in the guise of it being for their own security. MS tried before with INTEL to create a "trusted computing" with signed boot loaders. They got it, but it can be turned off in the BIOS -- for now. There's been some discussion regarding whether or not MS will allow it to be disabled in their future Surface Pros.
As to the first law of computer security, look at Ipads and Iphones - Apple hardware and software with a locked bootloader and constant updates to patch the exploits used to jailbreak them. Jailbreaks used to come out within a few days of the IOS release, then a few weeks... now, it's been 4 months since 8.1.3 was released -- no jailbreak yet. If you upgraded to a version you can't jailbreak, you now can't go back to an earlier version as Apple has stopped signing the old firmware.
But, Apple isn't sitting on its laurels. It's released 8.2, then 8.3, and soon 8.4 which is currently in beta. They're actively responding to jailbreaks - even calling the hacker teams by name that discovered the flaws and listing the specific exploits that have been patched. Hacker teams have even expressed their frustration as they've started to work on a possible exploit only to have Apple close the hole before releasing from BETA.
No one has a hardware hack for the Iphone or Ipad. It's all software exploits. Software will likely always have bugs, but Apple is hardening IOs against privilege escalation. I fear the low-hanging fruit is gone and jailbreaking will be a thing of the past for IOs in the very near future.
What's really telling is that my IT friends who used to jailbreak their Iphones (b/c it was cool... or they could hack it to install a browser with flash so they could watch HULU or some other such thing)... no longer care about jailbreaking their phones! They say it's too much trouble, they get stuck with older versions of IOs b/c the new ones aren't jailbroken yet... their TOS is invalidated if they have issues and want help at the Apple Store... and the Iphones really do everything they really want anyway without needing to jailbreak them. They've become accustomed to the DRM'd phone as-is!
If Apple can prevent jailbreaking their DRM'd Iphone and even get technically inclined (and pro-hacker, pro-pirate people at that) to not care their device is locked down, you bet MS could do the same for their Surface PRO and XBox.
But, it won't come as a hard sell. MS will say, "Here's an MS PC with MS OS, browser, office suite, games compatible with XBOX, Skype, etc etc... and it's locked down to only run our OS, our Apps, and a selection of approved apps through our store - and you must run all other non-approved programs in a sandbox/container/virtual machine so you can't get a virus from them. If you have a hardware or software issue, just call MS... and, if you upgrade to a new machine or have a hardware issue with your current one, your MS account has a record of your licenses and installation setup, so we can restore your PC (and your personal files are all backed up in the cloud for free through MS onedrive).
Don't think it won't happen -- Google practically did it themselves with Chromebooks.
Computers used to fill 2 story buildings, then a room, then a desktop PC... now most people are buying laptops that are desktop-replacements. Soon, our PCs may be as small as an Iphone. (the raspberry pi, arduino, mac mini, and a dozen other small form factors already exist). CPUs have incorporated math co-processors, modems, sound cards, gpus, northbridges, etc... it's only a matter of time before it's all system-on-a-chip the size of a credit card with a giant heat sink on it. There won't be any way to mod it.
As to your ports to repair issue... no. There will be DRM'ed firmware - eventually the entire OS will be in firmware. Think about current OS sizes. IOS and Android both exist in firmware. Windows is next. In fact, for the raspberry pi, it's almost there on a simple flash drive. If it gets corrupted, you plug it into another PC, download the latest signed firmware, flash it... and re-download all your apps which are attached to your account - just like a phone does today. Most phone repair places today just replace the glass or the batteries -- sometimes a SIM card issue (but SIMs are going software only soon, too!)
Ipads and Iphones are locked down with DRM, Google's looking to do the same eventually with Android. MS tried and failed with the original Surface, but they'll give it another go. the MPAA and RIAA really want their DRM, and so does MS, Apple and Intel. Google doesn't much care either way, but they have been designing their Chromebooks to be more difficult to override the boot lock as well.
Don't worry, though. It won't happen overnight. The megacorps are patient and worry about consumer backlash. All the pieces are there, though. MS just needs to sell its own PCs using XBOX and Surface Pro tech and lock the firmware with the trusted computing chip already in every machine and steer people towards the MS App store just like Google and Apple do with their app stores. Once the machines are as small as Iphones, just one PCB with a CPU/GPU hybrid core, there will be no way to physically hack it -- you will have to find buffer overflows or other exploits, but those will likely be undone on the next MS update... and you'll eventually be forced to get that MS update b/c some software will require it - or the OS itself will have auto-updates that a user can't override without another hack.
There will always be alternatives, but as PCs, notebooks, tablets, and phones become commodities; it's inevitable that only a few corporations will bother to produce them because you have to sell a massive number of them when you have razor-thin profit per unit. You'll eventually have your choice of Apple walled garden, Google walled garden, or MS walled garden... or some crap thing that will be the equivalent of today's random Chinese knock-off.