Can you elaborate a bit on this? because I can't find the relevance. Ruins aren't buildings so why would placing battlefield debris in/on them require an embarking action? I think what
OP is trying to ask is - Can you place terrain on top of other terrain, and if you can, will both pieces of terrain be moved when you cast Shifting Worldscape on the bottom piece?
I don't think there's a
RAW answer here as the rules concerning terrain as well as the rules covering Shifting Worldscape are very limited. There have been debates regarding whether or not you can move fortifications with the power since they would count as vehicles when you target them, there have been debates about whether the power would move entire connected sections of terrain (like a fortress of redemption or
ADL with a quad gun) and there have been debates about whether or not you can stack terrain on top of each other. Some forum searching on these topics here on Dakka should yield some more insight into the finer points of each debate, but I think it's safe to say you're going to have to agree on a house rule or talk to a
TO about it before you try it in a game.