https://groups.google.com/forum/#!topic/vim_dev/_SbMTGshzVc/...
Some choice posts:
- Bram (vim author's) response to whether he looked at existing implementation in neovim: https://groups.google.com/d/msg/vim_dev/_SbMTGshzVc/wXmJuL4P...
- Thiago (neovim author's) response to Bram, which was ignored: https://groups.google.com/d/msg/vim_dev/_SbMTGshzVc/XZEXxaxD...
There are lots of other instances of this exact interaction between neovim and vim over and over, it's infuriating. Neovim was started precisely for this reason, an async proposal was made (in 2014!!) which was rudely shut down and all efforts of collaboration were ignored.