>I believe it was a mistake to fracture the ecosystem with plugins that can only be used with neovim.

I hate to break this to you, but Vim itself is in the process of converting its runtime files into Vim9script (which is Vim specific), and many new Vim plugins are also being written in Vim9script.

Neovim has always supported "traditional" Vimscript, and has ported all runtime file changes from Vim (think filetype plugins, syntax highlighting, etc.). In fact, we explicitly request that any runtime file changes first go through Vim precisely because we want to keep the two projects aligned. But the more that Vim transitions to Vim9script, the less can be shared between the two projects. So unfortunately the "fracturing of the ecosystem" is not specific to Neovim.