I'm thinking Haruhi.
What I think is that haruhi will reject Hikaru kindly. Hikaru will be sad, but good-natured about it, and kiss Haruhi on the cheek at the precise moment Tamaki walks in. Basically, Hikaru will do more or less the same things Kaoru did to him. When Haruhi sees Tamaki and sees that he saw the kiss, she'll start blushing like hell, leave. Tamaki will be confused about his feelings, and Hikaru, like Kaoru did to him, will say, "It's not because you're her father. You love her as a woman," or something like that.
And I think that both he and Haruhi will keep quiet about their newly realized feelings.
As we know, Tamaki made a decision about whether or not to inherit his father's comapny, but we don't know what the decision is. Since he keeps going back to the Suou company to observe meetings, I think he will inherit it. And, I think that he and his father will return to France to continue the company there, since Tamaki's mother no longer needs life support. And when Haruhi figures out that Tamaki's leaving her behind... she'll do nothing.
Until her mother's kouhai has a talk with her and tells her to not wait. And then she'll go after him. and confess.
TA-DAAAAAA!!
as you can see, I've thought about this a lot. I need to do
something while waiting for the next chapter to come out, right? ^^.