What I figure is going to happen, is that either
A) Tamaki's father is planning a coup (Unlikely)
B) Tamaki's grandmother will grant him heir status or whatever, on the condition that he sever all ties with Haruhi, and will probably say she'll be expelled if he doesn't :x (Which would probably result in some sort of typical shoujo-esque confession of love somewhere or another from either Tamaki or Haruhi)
Either ways, I get the feeling that the manga might be ending soon :'(
I wouldn't be surprised if it has less than 15 chapters left :'(