I agree with you completely. The idea of a single language to rule the entire system is brilliant, and is something I wish others would consider putting their attention on - i.e. distro builders who compose a "Lua-only" stack, or a "Python-only" stack, and so on.. well, such things exist in Dockerland easily enough these days, but one wonder what it would be like if the 'modern desktop OSes' had this hit-one-key-and-access-code-anywhere mentality .. it has so much appeal over the current worm bucket o' mystery that is the modern OS 'distribution'/'package'/'bundle'/'module collection' ..

Smalltalk-80 and the resulting modern implementations of it follow this idea. Typically, the IDE/development tools come with the runtime environment and these allow the browse the system's code as well as inspect existing instances of object. There's also a primitive form of a built-in VCS allowing the viewing of earlier method versions and reverting to them. Finally, the underlying VM is written in a mixture of C and either Smalltalk or something resembling it.

It could even be C with something like the tiny c compiler. It can compile C at such ridiculous speeds it makes compile times practically irrelevant. I've never even been able to throw enough at it to know how fast it actually runs on a modern computer. SQLite and Lua both print a timing of 0.001 seconds (and that is both compiling and linking I think).

Emacs has what you called the hit-one-key-and-access-code-anywhere mentality, and I think part of the reason Emacs users tend to use it for much more than just editing text is exactly the appeal of an OS with that mentality.

wasn't that the idea with OLPC Sugar [http://wiki.laptop.org/go/Sugar]?

The whole desktop and apps in python and hackable.

It was definitely the idea with lisp machines (taken even further as they had hardware support for Lisp primitives and GC)

This is what makes http://www.redox-os.org/ an interesting project. Full stack Rust OS, which is probably the most advanced language you can use right now that can also bootstrap itself from ASM.

Talking about JITed OSes, that 92 thesis http://valerieaurora.org/synthesis/SynthesisOS/ is still a fun read.

It looks (at a quick glance) similar to an Oberon system.

I'm still really tempted by one of these http://oberonstation.x10.mx/

Yes! TempleOS seems a lot like a quirkier Oberon System actually—though sadly I've never used Oberon.

Man OberonStation looks tempting.

MirageOS does something similar with Ocaml. It uses this feature to compile Unikernals that run directly on Xen.