Yeah, just comint with elpy. There are some rough edges; I can't input multiline in the comint buffer (but can send it), and gives an error on the very first command, but otherwise works well.
If you connect your code buffer to an jupyter notebook via Emacs IPython Notebook [1] then you can hit C-c C-o (ein:console-open) which will launch a jupyter REPL.
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.
The REPL opened with org-babel-switch-to-session has been really buggy for me. Has it worked for you? Could just be because I'm using it with non-python kernels, which isn't well supported yet in general as far as I can tell.
I've only used it with a Python kernel so far, and doing eval on each or all blocks in the buffer (org-ctrl-c-ctrl-c, and org-babel-execute-buffer). Haven't had problems so far.
