EditorConfig is an editor-independent file format to describe
common editor configuration settings for a project, such as tab size,
character set, etc.

Many editors and IDEs support EditorConfig files (the web page has a
list); for Vim there's the editorconfig-vim plugin.

I think it would be a good idea to ship this with Vim by default. I
understand that there are many useful and popular plugins that Vim
could ship with by default, but most of those are "personal" plugins
that affect only the user's work-flow, whereas this plugin is one which
helps Vim users work well with other people (regardless of which editor
they use).

Modelines kind of solve the same problem, but are not perfect:

1. It's specific to Vim.
2. Needs to be added to every single file (potentially hundreds or
   thousands of them), which is kind of tedious and makes changing
   settings or adding new ones hard.
3. Modelines won't work when creating a new file.

Is this something you're willing to consider? The existing Vim plugin
works very well, but if changes need to be made then I can do that.