File name shouldn't change with version, that would mean eq2ui.xml or eq2ui_mainhud.xml would need to be updated to reflect it with every change, which is not good, especially if the user has multiple custom files.
I propose keeping the current convention but replacing "eq2ui" with "_(Author or UI name)" The reason for the _ before the author name is so that all custom files are at the top of the list when sorted by name. This was common practice for Morrowind modding.