While that would be nice in it's own way (if a bit too predictable) and that Reiji and Rei do get together, wasn't this whole thing for Reiji to get with one (or more) girls so as to pass on whatever it is in his bloodline that makes it possible to interact with Rei? Reiji's certainly going to pass on someday and unless there would be some kind of development that would allow Reiji to procreate with Rei then I suppose an eventual tragedy tag is in order I guess.
Though now that I think about it, at this point since Reiji confronted the lot about their feelings towards him wouldn't they now also be aware of him as a guy? And though that bit about Rei saying there is one at that time in love with him now however, what was one is now six? (Including probable stalker girl) That's some Xanatos Gambit right there
Well, if this is just going to end up as another fake harem like the others then I'm all for going after ara-ara onee-san type Ootori-senpai...