Patch 2.5.4 - Wrath of the Lich King Classic Interface Files
Blizzard just pushed the first build of 2.5.4 (the new TBC Classic phase) to the patch servers and it has the first hints that seem to confirm WotLK Classic is on its way.
The Classic clients separate interface files per "expansion" into separate folders, e.g. "Interface_Vanilla" for 1.x files and "Interface_TBC" for 2.x. This patch is the first that adds some files in the "Interface_Wrath" folder that have changes specific to WotLK, e.g. Deathknight support for the character creation screen as well as the blue buttons that are used on the login/character selection screens.
These files have likely been added as the various WoW clients use a shared code/content base, it is highly unlikely these files are going to be used in 2.5.4 and are likely for the WotLK Classic 3.4.x client instead.
Code:
Interface_Wrath\FrameXML\Bindings.xml
Interface_Wrath\GlueXML\GlueButtons.xml
Interface_Wrath\GlueXML\CharacterCreate.xml
Interface_Wrath\GlueXML\CharacterCreate.lua