FTA - Option 3: Using other existing REPL implementations: The authors looked at several alternatives like IPython, bpython, ptpython, and xonsh. While all the above are impressive projects, in the end PyREPL was chosen for its combination of maturity, feature set, and lack of additional dependencies. Another key factor was the alignment with PyPy’s implementation.
This really seems like a missed opportunity, instead of another repl that will only be used by developers (they even stated that as primary motivation) who can't install anything else, they could have taken a repl that would actually be widely used to integrate into other programs... Instead I suspect pyrepl will eventually experience the same fate as the current repl, i.e. it will languish with no development and get replaced again eventually because it has become to painful to adjust to changes in the rest of the language and changes in terminals.
Python is 150mo. Hard to justify that 10% of the lines of code, source of bugs and maintenance only go to the shell.