[justaj]

I don't understand. Can't NeoVim simply add the Vim9 interpreter and be a drop-in replacement for users that are migrating from Vim (9.0) this way?

[besnn00]

That would potentially make NeoVim slower, because you could have plugins that use Lua, plugins that use VimL and others that use Vim9. That means 3 runtimes which can contribute to latency.