As a Spacemacs user for over a year (and a neovim user for a few years before that, and a vim user for a few years before that), I find that spacemacs does a good job of emulating vim keybindings, but it isn't exactly right. Having neovim handling the keybindings and communicating what actions need to be taken back to emacs would let me have the great flexibility of emacs' plugin system, while retaining the vim keybindings in as authentic a manner as possible.