> I think Emacs today with the jitted Elisp interpreter it's able to do far more stuff than depending on external tools such as GNU coreutils, findutils and non-GNU Gnuplot.

The problem with doing everything in Elisp is the lack of threading. GNU Find can search down multiple directories in parallel, and an Elisp implementation of Grep would block the Emacs UI while searching. Until Elisp gets threading it will fundamentally be limited to either short bursts of computation or frustrating UX because of blocking (see also frustrations with Gnus).