Did you really feel like this didn't wrap things up with the three main girls? It is very clear what's going to happen: Kotooka and Washio end up together when they grow up, and Tsukasa is straight and dates boys, and they all still are friends.
I mean, you admit yourself that it doesn't wrap the entire story up, because the boys get nothing nearly as conclusive as Tsukasa channeling the author in prophetic soliloquy (except for the bonus chapter, which... appears to kill off any chance of a relationship between them at all?) but that's not quite what I was talking about.
I'll try to clarify: I think the author should have been able to tell this entire story, without a rushed axe ending, in half as many chapters as it got. Nothing about this story convinces me that it needed to be as long as it is, and certainly not longer, as was apparently the intention. I think 23 double-sized chapters should have been plenty of time for this series to live out a full and natural lifespan and come to a satisfying conclusion, but instead, it had to be cut short and rushed into an abrupt and incomplete ending.
Again, I fully admit: I did not read all of this story. Any assessment I make (aside from the obvious "I did not find it compelling enough to keep reading" ) is therefore quite incomplete, and can comfortably be disregarded. With that in mind, I still think this story had an incredibly unique and fascinatingly bittersweet core concept that's ultimately ruined by a bloat of self-indulgent navel-gazing. And that's a real shame.