This has been attempted before - with various levels of success. See "Plan 9 from Bell Labs"' acme.
In plan9, some of Unix' core concepts were abandoned. Including the 'one tool for one job' philosophy that is the basic underpinning of Unix. A prime example was particularly relevant for this discussion: acme.
Acme was
* A shell
* The window manager
* a file browser
* A text editor
* A hypertext browser (not sure if this included web browsing, it's been too long ago)
* A mail reader
all rolled into one binary. Basicly, *exactly* what you wish for. https://en.wikipedia.org/wiki/... kind of describes it.
Plan 9 didn't catch on for a number of reasons - some of those abandoned UNIX principles turned out to be important after all...