I assume it'll just add content cut from the original game.

@The switchify

TSLRM is a mod which restored most of the cut content,I wonder that would this DLC restore the droid planet,M4-78.

Nope, I'm assuming it'd just be really hard to install without support for it.

Absolutely not. The events of the Sith Lords can't be re-canonized because all the events preceding them that are intrinsic to the world being in the condition it's in at that point have all been retconned already. The Mandalorian Wars aren't the same anymore as well as Malachor V being completely different and so many other crucial things. Maybe a retelling will add a few things back but it'll never be fully re-canonized.

Well,I suppose to say that would the restored contents of TSLRM become the part of EU,It seems that it cased a lot of misunderstanding