That's pretty impressive considering the amount of change they made. Keeping it small, compatible and adding modern features and design .. I'm tempted to read their repository just to learn about project management.
For me the first one was that the plugin folder and the .vimrc file locations changed..
Comes from here:
https://github.com/ZyX-I/neovim/blob/42047acb4f07c689936b051...