One Thought I Had... (slight spoilers)
...and sorry if someone else has mentioned this; there are too many threads to check.
A big purpose / result of Tae-Suk's "house-crashing" is to fix things in the houses he enters, to make them better than they were before. (They massively clean up the photographer's house, for example.) No matter what theory you subscribe to as to what's going on, it seems that that's the end result in Sun-Hwa's house as well, even if she does end up back with her abusive husband. But this is the only house where he "fixes" a person, and not just inanimate objects (although each entry comes closer to that ideal; he fixes what remains of the old man's life in the last house that they enter together).
Just a thought while I mull over what I've just seen...