A CMS Built Using XML, SQlite, and PHP?

I've been a simple web designer for several years, but now I'm considering getting into web development by building a CMS with XML, SQLite, and PHP. Is there any logic to that? I don't see any current CMS's using this technology.

I've seen many articles saying XML or SQLite, but never together. My logic is this, I prefer XML because of it's custom tags ands sensible syntax. However, I wouldn't want to use XML for storing massive amounts of data. For that I would like to use SQLite because file based database. Which I think would be great for small to medium sites and would be easier for clients/users to setup on a shared server. For large sites, port it to MySQL.

Would this concept be viable?