Always interesting when a project stays 0 ver for so long- anyone close to the project know what would be considered significant enough for a "v1" release?
Possibly never: https://0ver.org/
AFAIK it's mostly about stabilizing the RPC API and Lua stdlib:
Maybe when `:!` works the way vi does and POSIX says it must.
Just kidding, that will never happen.
There is a roadmap and github issue tracking what is needed for 1.0.
https://github.com/neovim/neovim/issues/20451
https://neovim.io/roadmap/