This might be an odd thought, and I'm not sure how well I can express it, but...
So many times, romantic stories basically end after the confession. It's like, once the tension is gone, there's just nothing left to tell? But in this case, the confession happened off-page, before the story even began. Instead that sense of tension comes from their friends not knowing (which, personally, I think is starting to reach the level of cruelty, both toward their friends and for Nanoha). The "confession" in this case could be the point where they tell their friends.
So, on the one hand, I'm looking forward to the day their friends find out, but on the other hand, I have the feeling that will be more or less the end of their tale. Futaribeya certainly shows that kind of tension is not necessary to carry a series, but it's pretty uncommon to go without, and I think the character of Hana ni Arashi would change a lot if that happened.