I have to store many XML documents recognized with a unique title, and keep an eye on their versions. I have to come with an use of every document (read, update, remove) through some Peaceful API. I have to maintain access control (read/write permissions) for each document (or categories of them).

Can there be any solution available on the market of these needs?

Btw, other extra features could be welcome, like XSD-validation of each and every new incoming change.

This is exactly what I have found to date:

You can consider CouchDB: http://www.couch.io/

You can try github.com/dscape/facade to have an free project using Relaxation + versioning. I am doing JSON but XML in MarkLogic could be even simpler