Looks like that just calls make-comint-in-buffer eventually[1] with some fancy stuff to make sure it connects to the same jupyter server as being used for ein. Not sure I see a lot of utility there if I'm just wanting to run a jupyter REPL next to a regular code buffer or e.g. org-mode.

[1] https://github.com/millejoh/emacs-ipython-notebook/blob/cfd0...