A useful piece of information for the folks scratching their heads about how a harem could possibly work: the definition of a harem on this site is the MC involved with three or more LIs who all know about (and presumably approve of) each other. The harem does not need to include all LIs in a game. The members of the harem do not need to be involved with each other although they can be.
Using that definition, I think there are a few harem combinations that could be possible. For one, while I don't see Ashley wanting to share MC with just anyone, I kinda think she'd be okay with SungJi and if Vicky successfully integrates into their group, she might be okay with her as well. For another, I could totally see Jenny being okay with MC being involved with her little "family" unit. In fact, even when MC is on her route with max or at least close to max points, she maneuvers him toward one or the other of the girls on a couple of occasions. Third, we haven't seen a lot of interactions with the older girls, but maybe something along these lines could emerge among Elizabeth, Heather, Susan and the Librarian, blanking on her name atm.
The dev put the tag there for a reason. We might as well just wait to see what he has in mind.