CI4 CMS

I think CMS is the tip of the iceberg. Before that, there should be a shared database design, a shared vision about how to dinamically route the calls and so on...
Eventually it comes the CMS.

But you mean all of that, then YES, I believe it would be great. Hard to do, but great

Usually such a "standard" come from a very sharp guy that write a very sharp book about the framework, adding practice to theory.

In this moment you can find a lot of tutorials "How to create a blog with CI4". Should anyone be writing a book "How to create a website and a CMS with CI4" it will probably be the point to start from.

I'd stand by, for a while. But this is my very humble opinion.