Is there a way to open a GnuPG encrypted file with
neovim so that one can read/edit it and on write the file is re-encrypted?
I did a little research and it seems that the only option right now is the one mentioned by @grodzik: you need to configure
gpg-agent. Quoting Thiago de Arruda (Neovim lead developer):
I'm a long time vim-gnupg user and have been using it with neovim since day 1. I never had problems because I use gpg-agent which by defaults displays a x11 prompt to get the password (the GPG_TTY warning can be safely ignored).
In the same thread the vim-pgp author has shared his progress on making the plug-in compatible with Neovim. I think it will take a while but lately he has been contributing to Neovim (in fact the last Neovim commit is authored by him) so it's just matter of time.