This sounds like a rant from a person not really acquainted with operating systems.

> Why can I dock and undock tabs in my web browser or in my file manager, but I can't dock a tab between the two apps?

How would this even be semantically meaningful? What about top-level components like menus which are completely different?

> Why can't I have a file in two places at once on my filesystem?

Umm, soft and hard links do exactly that.

> Why can't I speak commands to my computer

Cortana takes a shot at that. Personally, I don't even want to try out the feature until it has the level of comprehension corresponding to a human. Otherwise, I'll just be guessing how to spell out my sentences / commands..

> or have it watch as I draw signs in the air, or better yet watch as I work to tell me when I'm tired and should take a break.

Because these are hard problems in computer vision, unrelated to operating systems.

> Each application has its own part of the filesystem

Yes, I wouldn't want to give up on that. It's orderly.

> its own config system, and its own preferences, database

Well, Windows unifies this in the registry. It's somewhat unpopular.

> Traditional filesystems are hierarchical, slow to search, and don't natively store all of the metadata we need.

NTFS can store extended metadata + arbitrary data in alternate data streams. Doesn't seem to be used very much.

> I'd like to pipe my Skype call to a video analysis service while I'm chatting, but I can't really run a video stream through awk or sed.

The video stream is a stream of bytes. Skype interprets it and constructs a video from that byte stream. Does he suggest that this interpreter should be part of the kernel? That there is one single video streaming protocol that fits all purposes?

> Native Applications are heavy weight,

Um? I have yet to see a "non-native" application that is as snappy as a native one.

> take a long time to develop and very siloed.

Any application takes a long time to develop. If you care about stability, crash recovery, etc.

> Wouldn't it be easier to build a new email client if the database was already built for you?

Exists, integrated in the Windows OS: https://en.wikipedia.org/wiki/Extensible_Storage_Engine

> The UI would only be a few lines of code.

It's logic behind the UI that's complicated, not building the UI itself (heck, you can just draw it if you use C# or VB).

> If you want to make a program that works with the song database you have to reverse engineer iTunes DB format

Even if the hypothetical document DB existed, how would one program know about the schema of other programs? Or schema versioning, or...? The problems with proprietary formats won't just disappear, it'll just become easier to do the wrong thing based on misinterpretation of the other program's schema.

> Message Bus [...] All applications become small modules that communicate through the message bus for everything.

COM, DCOM, CORBA... The first two are made user-friendly on Windows by C#. Don't know whether it's possible to snoop on COM messages, but given the thickness of the documentation on COM, I'd say the answer is "yes".

> However, this also means we have to rebuild everything from scratch.

Yes. Windows already exposes an insane amount of helper objects as COM components.

> You could build a new email frontend in an afternoon...

In which alternate universe?

> I really like the commandline as an interface sometimes, it's the pure text nature that bothers me. Instead of chaining CLI apps together with text streams we need something richer, like serialized object streams (think JSON but more efficient).

He should read up on Powershell. It's also extensible and can directly invoke COM components (+ all of the .net framework).

> System Side Semantic Keybindings

That one may be original. I think KDE has something like this.

> The clipboard should be visible on screen as some sort of a shelf that shows the recent items I've copied.

IIRC, I've seen something like this in KDE. Earlier versions of Windows had some "clipboard manager" too, though it seems to have disappeared in new versions. Plenty of freeware ones though.

> In the new system all applications are tiny isolated things which only know what the system tells them.

That's how Windows UWP applications behave. Appstore ones too. IIRC, some old, then-mainstream OS-es tried the kind of separation and it didn't work well with users. Sometimes you want to share data between isolation domains.

> None of this is New

No, and it seems that, feature-wise, Windows is closest to his dream OS. Now he just needs to convince programmers to use the features that are already there :-)