Sounds like the Dynabook goal rather overlaps with that
of Lisp Machines. The idea of a single system that allows
you to modify any part at runtime, inspect any part, or
drop into a debugger anywhere is extremely powerful and
wonderful to work with.
Emacs gets quite close to this, but... it's Emacs lisp. I've
used worse languages, but elisp was not intended to be a
general purpose application programming language. Smalltalk
is, which is why Pharo excites me.
Once you start 'living' in a single environment, you customise
it to meet your needs and can contribute the reusable parts to
the wider community. This produces a virtuous circle of the
tools getting better. A package manager that makes it easy to
distribute your work is crucial in this.