Some early preview of BFA API changes:
I dont have Alpha access, and I just had a look at UI source exported by other: https://github.com/tomrus88/BlizzardInterfaceCode

Obviously, the API hasn't been completed.

There are more C_XXX functions added. The most interesting ones are:
C_Item

In FrameXML/ObjectAPI/Item.lua, some useful utility functions related to item info are added.
"ItemEventListener" -- Request item info and run callback when the item info is fetched.

I like the objective code style in ObjectAPI folder. This is the way to go in RCv3.

new in UIDropdownMenu:
info.owner = [Frame] -- Dropdown frame that "owns" the current dropdownlist
info.customFrame = frame -- Allows this button to be a completely custom frame, should inherit from UIDropDownCustomMenuEntryTemplate and override appropriate methods.