DITA is, for all intents and purposes, an XML file format that has a particular series of tools built around it. It's mainly used as a markup language for documents, with an accompanying set of processing tools.
Is this something we need a site for? It feels like this is really a bigger site than just this. There are a number of document markup languages (DocBook and TeX/LaTeX among them, though the latter also includes presentation information); we shouldn't have separate sites for each. I know TeX/etc already have their own site, but that's not an example we should be following.
HTML is already effectively covered by Stack Overflow, as it interacts with programming languages (and stylesheets) enough to be considered programming. But most of the rest (DITA, Docbook, Markdown, etc) aren't covered. I'm thinking that we should have a unified site for all of these kinds of document markup languages.
Note that we stick all programming languages on the same site (Stack Overflow). So I don't see why DITA is so special in the document markup languages domain to need its own site.