WowAce

In LibUIDropDownMenu.lua line 73 you should probably set the initializeHelper function to be a local function.

In the LibEasyMenu.lua if you want the EasyMenu function to be part of the LibUIDropDownMenu-4.0 library you should replace the lib: with LibDD: as how it currently is written it is creating a separate LibEasyMenu-2.0 library

Also you need to move the easyMenu_Initialize function to before the LibDD:EasyMenu function. Where it is currently does not trigger when the easy menu is called.  Alternately you can remove the easyMenu_Initialize function and use instead

LibDD:UIDropDownMenu_Initialize(menuFrame, function(...) LibDD:EasyMenu_Initialize( ... ) end, displayMode, nil, menuList);

Regarding to initializeHelper(), you are right, this one should be set to local function.

As for EasyMenu parts, I have moved it now. Please help to test it.