I'll move my proposal from the comments to an answer so that people can vote on it.
I propose to rename it to desktop-files, because:
- Having a leading dot makes sense only when referencing desktop files by their extension; since the tag has to change but the extension won't change, there's no reason to prepend a dot to whatever nomenclature we're gonna use, since obviously it will never match the extension *;
- "Desktop files" is how they're referenced in the Ubuntu Community Wiki. Using the same name will allow to keep consistency across the Ubuntu Community Wiki and the site.
- This introduces two possible choices: using the singularized desktop-file or the pluralized desktop-files. I'd choose the pluralized desktop-files in order to be able to group toghether questions about a specific desktop file and questions about desktop files in general, which makes sense only to group toghether under a single tag.
* Before someone argues that beside this reasoning .desktop-files makes equal sense to desktop-files: yes, mostly. But the problem is that one of the two must be preferred. Since they're both good, digressing into nitpickeries, putting the thing into what I think is the right perspective, to make a comparison, you don't say e.g. "I have a dot-mp4 file", you say "I have an mp4 file".