We already knew about some major changes about addons. As far as i could see on curse.com comments too, most of the addons will have to be rebuild not only modified for the upcoming patch. I guess the addons authors will understand this better that us.
SourceAlong with Patch 2.4 we will be releasing a revamped in-game Interface Options screen. Most of the systems that interact with the current Interface Options screen have seen some code changes as a result. The new architecture for the system should allow AddOn authors to modify its contents without the taint issues presented by the current Interface Options system.
Additionally, this new system will contain an area for AddOn authors to present their own configuration options to players with a custom heading, subcategories, and frames. I'd like to encourage authors interested in utilizing these features to try the new system on the PTRs before Patch 2.4 is released. Basic details on how to use this system can be found in code comments in Blizzard_InterfaceUI.lua.
Please be aware that AddOns that interact with the Interface Options screen, modify it, or change the way that its options affect other systems within the game will need to be updated with the release of Patch 2.4.