I didn’t know that Neovim was a complete rewrite, thanks for sharing. The fact that I didn’t know while actively using nvim is a testament to the quality of compatibility they deliver.
I don't believe it's a full rewrite. From Neovim's Vision statement:
"Neovim is a refactor, and sometimes redactor, in the tradition of Vim (which itself derives from Stevie). It is not a rewrite but a continuation and extension of Vim."
"Neovim is a refactor, and sometimes redactor, in the tradition of Vim (which itself derives from Stevie). It is not a rewrite but a continuation and extension of Vim."
https://neovim.io/charter/