Is my understanding that the majority of announced units and abilities that don't quite make it into the game will still be made available in scumedit correct?
Wow, that sentence kind of messes with your brain, doesn't it?

They said that some of the old units from SC2 might be in the new editor, along with the joke units such as Tauren Marine.

I think it would be awesome if they had the original SC units in the editor.

Blizzard has stated that most development units and many units from original sc will be in the editor. I imagine that this is a low priority for the art team and as long as they don't have something better to do, they will develop these units for the editor. There have been screenshots of the wraith.