I know you listed Lua already, but it's important to stress that. Bram _did not_ want Lua as the main scripting language, and created Vim9 Script as a "better VimScript" instead. That's a stark difference in the direction for the project, and it signals to me that Vim is not meant to reintegrate with Neovim. It's no longer a question of Vim catching up with Neovim.
However, this was Bram's vision. We don't know how the new leadership will affect that.