I want to be able to mark pages in certain namespace which kind of draft (how "ripe", roughly saying) is this page.
I want tree different kinds of drafts.
I also want to highlight internal links to these pages with different color dependently on draft status.
Is it possible?
I don't think an extension for this feature has been made as of yet. (You could try searching for it, but I'm sure you have)
That being said, everything is possible if you know how to write code!
On each page, you can use a template and inside the according templates, you can use a category so that pages, which include the template, automatically get added to the category.
Highlighting of links based on the inclusion of a template is not possible currently I think. But the basic principle - automatically render a page again, if another page got changed - already is included for MediaWiki. This is exactly what is happening, when a new page gets created, which is linked in another page. In this case this other page gets purged automatically. Anyway, doing such purges, potentially to a really big number of pages, is an expensive operation...
